Processes for treating fly ashes

ABSTRACT

There are provided processes for treating fly ash. For example, the processes can comprise leaching fly ash with HCl so as to obtain a leachate comprising aluminum ions and a solid, and separating the solid from the leachate; reacting the leachate with HCl so as to obtain a liquid and a precipitate comprising the aluminum ions in the form of AlCl 3 , and separating the precipitate from the liquid; and heating the precipitate under conditions effective for converting AlCl 3  into Al 2 O 3  and optionally recovering gaseous HCl so-produced.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 35 USC 371 national stage entry of PCT/CA2013/000218 filed on Mar. 11, 2013 and which claims priority on U.S. 61/617,422 filed on Mar. 29, 2012; and on U.S. 61/706,028 filed on Sep. 26, 2012. These documents are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to improvements in the field of processes for treating industrial waste materials. For example, it relates to processes for treating fly ash. For example, these processes can be effective for extracting various materials from fly ash such as alumina and various metal oxides, silica, and rare earths, etc.

BACKGROUND OF THE DISCLOSURE

fly ash is one of the residues generated in combustion. It comprises fine particles that rise with the flue gases. Ash which does not rise is termed bottom ash. Fly ash material can solidify while suspended in the exhaust gases and is collected by electrostatic precipitators Of filter bags. Since the particles solidify while suspended in the exhaust gases, fly ash particles can be generally spherical in shape and range in size from 0.5 μm to 100 μm. Fly ash can comprise silicon dioxide (SiO₂) (which can be present in two forms: amorphous, which is rounded and smooth, and crystalline, which is sharp, pointed and hazardous); aluminium oxide (Al₂O₃ ) and iron oxide (Fe₂O₃), Fly ashes can also comprise calcium oxide (CaO), Fly ashes can also be highly heterogeneous. They can comprise a mixture of glassy particles with various identifiable components.

For example, fly ash can refer to ash produced during combustion of coal. Depending upon the source and makeup of the coal being burned, the components of fly ash vary considerably,

In the past, fly ash was generally released into the atmosphere, but pollution control equipment mandated in recent decades now require that it be captured prior to release. Fly ash is generally captured by electrostatic precipitators or other particle filtration equipment before the flue gases reach the chimneys of coal-fired power plants, and together with bottom ash removed from the bottom of the furnace is in this case jointly known as coal ash. For example, in the US, fly ash can be generally stored at coal power plants or placed in landfills. About 43 percent is recycled,^([3]) often used to supplement Portland cement in concrete production. However, some scientists have expressed health concerns about this.

In the past, fly ash produced from coal combustion was simply entrained in flue gases and dispersed into the atmosphere. This created environmental and health concerns that prompted laws which have reduced fly ash emissions to less than 1 percent of ash produced. Worldwide, more than 65% of fly ash produced from coal power stations is disposed of in landfills and ash ponds. The recycling of fly ash has become an increasing concern in recent years due to increasing landfill costs and current interest in sustainable development. As of 2005, U.S. coal-fired power plants reported producing 71.1 million tons of fly ash, of which 29.1 million tons were reused in various applications. If the nearly 42 million tons of unused fly ash had been recycled, it would have reduced the need for approximately 27,500 acre·ft (33,900,000 m³) of landfill space.

There is thus a need for at least an alternative process for treating, recycling and/or valorizing fly ash.

SUMMARY OF THE DISCLOSURE

According to one aspect, there is provided a process for preparing alumina and optionally other products, the process comprising:

-   -   leaching an aluminum-containing material with HCl so as to         obtain a leachate comprising aluminum ions and a solid, and         separating the solid from the leachate;     -   reacting the leachate with HCl so as to obtain a liquid and a         precipitate comprising the aluminum ions in the form of AlCl₃,         and separating the precipitate from the liquid;     -   heating the precipitate under conditions effective for         converting AlCl₃ into Al₂O₃ and recovering gaseous HCl         so-produced; and     -   recycling the gaseous HCl so-produced by contacting it with         water so as to obtain a composition having a concentration         higher than HCl azeotrope concentration (20.2 weight %) and         reacting the composition with a further quantity of         aluminum-containing material so as to leaching it.

According to another aspect, there is provided a process for preparing alumina and optionally other products, the process comprising:

-   -   leaching an aluminum-containing material with HCl so as to         obtain a leachate comprising aluminum ions and a solid, and         separating the solid from the leachate;     -   reacting the leachate with HCl so as to obtain a liquid and a         precipitate comprising the aluminum ions in the form of AlCl₃,         and separating the precipitate from the liquid;     -   heating the precipitate under conditions effective for         converting AlCl₃ into Al₂O₃ and recovering gaseous HCl         so-produced; and     -   recycling the gaseous HCl so-produced by contacting it with         water so as to obtain a composition having a concentration of         about 18 to about 45 weight % or about 25 to about 45 weight %         and reacting the composition with a further quantity of         aluminum-containing material so as to leaching it.

According to another aspect, there is provided a process for preparing alumina and optionally other products, the process comprising:

-   -   leaching an aluminum-containing material with HCl so as to         obtain a leachate comprising aluminum ions and a solid, and         separating the solid from the leachate;     -   reacting the leachate with HCl so as to obtain a liquid and a         precipitate comprising the aluminum ions in the form of AlCl₃,         and separating the precipitate from the liquid;     -   heating the precipitate under conditions effective for         converting AlCl₃ into Al₂O₃ and recovering gaseous HCl         so-produced; and     -   recycling the gaseous HCl so-produced by contacting it with         water so as to obtain a composition having a concentration of         about 18 to about 45 weight % or about 25 to about 45 weight %         and using the composition for leaching the aluminum-containing         material.

According to another aspect, there is provided a process for preparing alumina and optionally other products, the process comprising:

-   -   leaching an aluminum-containing material with HCl so as to         obtain a leachate comprising aluminum ions and a solid, and         separating the solid from the leachate;     -   reacting the leachate with HCl so as to obtain a liquid and a         precipitate comprising the aluminum ions in the form of AlCl₃,         and separating the precipitate from the liquid;     -   heating the precipitate under conditions effective for         converting AlCl₃ into Al₂O₃ and recovering gaseous HCl         so-produced; and     -   recycling the gaseous HCl so-produced by contacting it with the         leachate so as to precipitate the aluminum ions in the form of         AlCl₃.6H₂O.

According to another aspect, there is provided a process for preparing alumina and optionally other products, the process comprising:

-   -   leaching an aluminum-containing material with HCl so as to         obtain a leachate comprising aluminum ions and a solid, and         separating the solid from the leachate;     -   reacting the leachate with HCl so as to obtain a liquid and a         precipitate comprising the aluminum ions in the form of AlCl₃,         and separating the precipitate from the liquid; and     -   heating the precipitate under conditions effective for         converting AlCl₃ into Al₂O₃.

According to another aspect, there is provided a process for preparing alumina and optionally other products, the process comprising:

-   -   leaching an aluminum-containing material with HCl so as to         obtain a leachate comprising aluminum ions and a solid, and         separating the solid from the leachate;     -   reacting the leachate with HCl so as to obtain a liquid and a         precipitate comprising the aluminum ions in the form of AlCl₃,         and separating the precipitate from the liquid; and     -   heating the precipitate under conditions effective for         converting AlCl₃ into Al₂O₃ and optionally recovering gaseous         HCl so-produced.

According to one aspect, there is provided a process for preparing aluminum and optionally other products, the process comprising:

-   -   leaching an aluminum-containing material with HCl so as to         obtain a leachate comprising aluminum ions and a solid, and         separating the solid from the leachate;     -   reacting the leachate with HCl so as to obtain a liquid and a         precipitate comprising the aluminum ions in the form of AlCl₃,         and separating the precipitate from the liquid;     -   heating the precipitate under conditions effective for         converting AlCl₃ into Al₂O₃; and     -   converting Al₂O₃ into aluminum.

According to another aspect, there is provided a process for preparing aluminum and optionally other products, the process comprising:

-   -   leaching an aluminum-containing material with HCl so as to         obtain a leachate comprising aluminum ions and a solid, and         separating the solid from the leachate;     -   reacting the leachate with HCl so as to obtain a liquid and a         precipitate comprising the aluminum ions in the form of AlCl₃,         and separating the precipitate from the liquid;     -   heating the precipitate under conditions effective for         converting AlCl₃ into Al₂O₃ and optionally recovering gaseous         HCl so-produced; and     -   converting Al₂O₃ into aluminum.

According to another aspect, there is provided a process for preparing various products, the process comprising:

-   -   leaching an aluminum-containing material comprising a first         metal with HCl so as to obtain a leachate comprising ions of the         first metal and a solid, and separating the solid from the         leachate;     -   reacting the leachate with HCl so as to obtain a liquid and a         precipitate comprising a chloride of the first metal, and         separating the precipitate from the liquid; and     -   heating the precipitate under conditions effective for         converting the chloride of the first metal into an oxide of the         first metal.

According to another aspect, there is provided a process for preparing various products, the process comprising:

-   -   leaching an aluminum-containing material comprising a first         metal with an acid so as to obtain a leachate comprising ions of         the first metal and a solid, and separating the solid from the         leachate;     -   substantially selectively removing ions of the first metal from         the leachate, thereby obtaining a composition; and     -   substantially selectively removing ions of a second metal from         the composition.

According to another aspect, there is a process for treating an aluminum-containing material comprising:

-   -   leaching fly ash with an acid so as to obtain a leachate and a         solid residue, and separating the leachate from the solid         residue;     -   at least partially removing iron ions from the leachate by         substantially selectively precipitating the iron ions at a pH         greater than 10 by reacting the leachate with a base and at         least partially removing the precipitated iron ions from the         leachate, thereby obtaining an Al-rich composition comprising         Al³⁺ ions;     -   optionally purifying the Al³⁺ ions; and     -   converting the Al³⁺ ions into alumina.

According to another aspect, there is a process for treating an aluminum-containing material comprising:

-   -   leaching the aluminum-containing material with an acid so as to         obtain a leachate and a solid residue, and separating the         leachate from the solid residue;     -   at least partially removing iron ions from the leachate by         substantially selectively precipitating the iron ions at a pH of         about 3 to about 6 by reacting the leachate with a base and at         least partially removing the precipitated iron ions from the         leachate, thereby obtaining an Al-rich composition comprising         Al³⁺ ions;     -   optionally purifying the Al³⁺ ions; and     -   converting the Al³⁺ ions into alumina.

BRIEF DESCRIPTION OF DRAWINGS

In the following drawings, which represent by way of example only, various embodiments of the disclosure:

FIG. 1 shows a bloc diagram of an example of process for preparing alumina and various other products according to the present disclosure;

FIG. 2 is an extraction curve for Al and Fe in which the extraction percentage is expressed as a function of a leaching time in a process according to an example of the present application;

FIG. 3 shows a bloc diagram of another example of process for preparing alumina and various other products according to the present disclosure;

FIG. 4 is a schematic representation of an example of a process for purifying/concentrating HCl according to the present disclosure;

FIG. 5 is a schematic representation of an example of a process for purifying/concentrating HCl according to the present disclosure;

FIG. 6 shows another bloc diagram of an example of process for preparing alumina and various other products according to the present disclosure; and

FIG. 7 shows another bloc diagram of an example of process for preparing alumina and various other products according to the present disclosure.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The following non-limiting examples further illustrate the technology described in the present disclosure.

The aluminum-containing material can be for example chosen from aluminum-containing ores (such as aluminosillicate minerals, clays, argillite, nepheline, mudstone, beryl, cryolite, garnet, spinel, bauxite, kaolin or mixtures thereof can be used). The aluminum-containing material can also be a recycled industrial aluminum-containing material such as slag, red mud or fly ash.

The expression “red mud” as used herein refers, for example, to an industrial waste product generated during the production of alumina. For example, such a waste product can comprise silica, aluminum, iron, calcium, and optionally titanium. It can also comprise an array of minor constituents such as Na, K, Cr, V, Ni, Ba, Cu, Mn, Pb, and/or Zn etc. For example, red mud can comprises about 15 to about 80% by weight of Fe₂O₃, about 1 to about 35% by weight Al₂O₃, about 1 to about 65% by weight of SiO₂, about 1 to about 20% by weight of Na₂O, about 1 to about 20% by weight of CaO, and from 0 to about 35% by weight of TiO₂. According to another example, red mud can comprise about 30 to about 65% by weight of Fe₂O₃, about 10 to about 20% by weight Al₂O₃, about 3 to about 50% by weight of SiO₂, about 2 to about 10% by weight of Na₂O, about 2 to about 8% by weight of CaO, and from 0 to about 25% by weight of TiO₂.

The expression “fly ashes” or “fly ash” as used herein refers, for example, to an industrial waste product generated in combustion. For example, such a waste product can contain various elements such as silica, oxygen, aluminum, iron, calcium. For example, fly ash can comprise silicon dioxide (SiO₂) and aluminium oxide (Al₂O₃). For example, fly ash can further comprises calcium oxide (CaO) and/or iron oxide (Fe₂O₃). For example fly ash can comprise fine particles that rise with flue gases. For example, fly ash can be produced during combustion of coal. For example, fly ash can also comprise at least one element chosen from arsenic, beryllium, boron, cadmium, chromium, chromium VI, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, and/or vanadium. For example, fly ash can also comprise rare earth elements and rare metals. For example, fly ash can be considered as an aluminum-containing material. For example, fly ash can comprise about 40 to about 50% by weight SiO₂, about 20 to about 30% by weight Al₂O₃, about 15 about 25% by weight Fe₂O₃, about 1 to about 6% by weight Ca₂O, about 0 to about 2% by weight MgO, about 0 to about 2% Na₂O and about 1 to about 4% K₂O

The expression “rare earth element” (also described as “REE”) as used herein refers, for example, to a rare element chosen from scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. The expression “rare metals” as used herein refers, for example, to rare metals chosen from indium, zirconium, lithium, and gallium. These rare earth elements and rare metals can be in various form such as the elemental form (or metallic form), under the form of chlorides, oxides, hydroxides etc. The expression “rare earths” as used in the present disclosure as a synonym of “rare earth elements and rare metals” that is described above.

The expression “at least one iron chloride” as used herein refers to FeCl₂, FeCl₃ or a mixture thereof.

The term “hematite” as used herein refers, for example, to a compound comprising α-Fe₂O₃.

The expression “iron ions” as used herein refers, for example to ions comprising to at least one type of iron ion chosen from all possible forms of Fe ions. For example, the at least one type of iron ion can be Fe²⁺, Fe³⁺, or a mixture thereof.

The expression “aluminum ions” as used herein refers, for example to ions comprising to at least one type of aluminum ion chosen from all possible forms of Al ions. For example, the at least one type of aluminum ion can be Al³⁺.

The expression “at least one aluminum ion”, as used herein refers, for example, to at least one type of aluminum ion chosen from all possible forms of Al ions. For example, the at least one aluminum ion can be Al³⁺.

The expression “at least one iron ion”, as used herein refers, for example, to at least one type of iron ion chosen from all possible forms of Fe ions. For example, the at least one iron ion can be Fe²⁺, Fe³⁺, or a mixture thereof.

The expression “at least one precipitated iron ion”, as used herein refers, for example, to at least one type of iron ion chosen from all possible forms of Fe ions that was precipitated in a solid form. For example, the at least one iron ion present in such a precipitate can be Fe²⁺, Fe³⁺, or a mixture thereof.

Terms of degree such as “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% or at least ±10% of the modified term if this deviation would not negate the meaning of the word it modifies.

For example, the material can be leached with HCl having a concentration of about 10 to about 50 weight %, about 15 to about 45 weight %, of about 18 to about 45 weight % of about 18 to about 32 weight %, of about 20 to about 45 weight %, of about 25 to about 45 weight %, of about 26 to about 42 weight %, of about 28 to about 40 weight %, of about 30 to about 38 weight %, or between 25 and 36 weight %. For example, HCl at about 18 wt % or about 32 wt % can be used.

Leaching can also be carried out by adding dry highly concentrated acid (for example, 85%, 90% or 95%) in gas phase into the aqueous solution. Alternatively, leaching can also be carried out by using a weak acid solution (for example <3 wt %).

For example, leaching can be carried out by using HCl having a concentration of about 18 to about 32 wt % in a first reactor and then, by using HCl having concentration of about 90 to about 95% (gaseous) in a second reactor.

For example, leaching can be carried out by using HCl having a concentration of about 18 to about 32 wt % in a first reactor then, by using HCl having concentration of about 90 to about 95% (gaseous) in a second reactor; and by using HCl having concentration of about 90 to about 95% (gaseous) in a third reactor.

For example, leaching can be carried out under an inert gas atmosphere (for example argon or nitrogen).

For example, leaching can be carried out under an atmosphere of NH₃.

For example, the material can be leached at a temperature of about 125 to about 225° C., about 150 to about 200° C., about 160 to about 190° C., about 185 to about 190° C., about 160 to about 180° C., about 160 to about 175° C., or about 165 to about 170° C.

For example, the material can be leached at a pressure of about 4 to about 10 barg, about 4 to about 8 barg, or about 5 to about 6 barg.

The leaching can be carried out under pressure (for example greater than atmospheric pressure) into an autoclave. For example, it can be carried out at a pressure of about 5 KPa to about 850 KPa, about 50 KPa to about 800 KPa, about 100 KPa to about 750 KPa, about 150 KPa to about 700 KPa, about 200 KPa to about 600 KPa, or about 250 KPa to about 500 KPa. The leaching can be carried out at a temperature of at least 80° C., at least 90° C., or about 100° C. to about 110° C. In certain cases, it can be done at higher temperatures.

The leaching can also be carried out under pressure. For example, the pressure can be about 100 to about 300 or about 150 to about 200 psig. The leaching can be carried out for about 30 minutes to about 5 hours. It can be carried out at a temperature of about 60° C. to about 200° C.

For example, the processes can further comprise recycling the gaseous HCl so-produced by contacting it with water so as to obtain a composition having a concentration of about 18 to about 45 weight % or 25 to about 45 weight %.

For example, the processes can further comprise recycling the gaseous HCl so-produced by contacting it with water so as to obtain a composition having a concentration of about 18 to about 45 weight %, about 26 to about 42 weight %, about 28 to about 40 weight %, about 30 to about 38 weight %, between 18 and 36 weight %, between 19 and 36 weight %, between 25 and 36 weight % or about 25 to about 45 weight % and optionally using the composition for leaching the material.

For example, the liquid can comprise iron chloride. Iron chloride can comprise at least one of FeCl₂, FeCl₃, and a mixture thereof.

For example, the liquid can have an iron chloride concentration of at least 30% by weight; and can then be hydrolyzed at a temperature of about 155 to about 350° C.

For example, the liquid can be concentrated to a concentrated liquid having an iron chloride concentration of at least 30% by weight; and then the iron chloride can be hydrolyzed at a temperature of about 155 to about 350° C. while maintaining a ferric chloride concentration at a level of at least 65% by weight, to generate a composition comprising a liquid and precipitated hematite, and recovering the hematite.

For example, non-hydrolysable elements with hematite can be concentrated back to a concentration of about 0.125 to about 52% wt. in circulation loop in view of selective extraction.

For example, the liquid can be concentrated to a concentrated liquid having a concentration of the at least one iron chloride of at least 30% by weight; and then hydrolyzed at a temperature of about 155 to about 350° C.

For example, the liquid can be concentrated to a concentrated liquid having a concentration of the at least one iron chloride of at least 30% by weight; and then the at least one iron chloride is hydrolyzed at a temperature of about 155 to about 350° C. while maintaining a ferric chloride concentration at a level of at least 65% by weight, to generate a composition comprising a liquid and precipitated hematite, and recovering the hematite.

For example, the liquid can be concentrated to a concentrated liquid having a concentration of the at least one iron chloride of at least 30% by weight; and then the at least one iron chloride is hydrolyzed at a temperature of about 155 to about 350° C. while maintaining a ferric chloride concentration at a level of at least 65% by weight, to generate a composition comprising a liquid and precipitated hematite; recovering the hematite; and recovering rare earth elements and/or rare metals from the liquid.

For example, the at least one iron chloride can be hydrolyzed at a temperature of about, 150 to about 175, 155 to about 170 or 165 to about 170° C.

For example, the liquid can be concentrated to a concentrated liquid having an iron chloride concentration of at least 30% by weight; and then the iron chloride can be hydrolyzed at a temperature of about 155 to about 350° C. while maintaining a ferric chloride concentration at a level of at least 65% by weight, to generate a composition comprising a liquid and precipitated hematite; recovering the hematite; and recovering rare earth elements and/or rare metals from the liquid.

For example, the processes can further comprise, after recovery of the rare earth elements and/or rare metals, reacting the liquid with HCl so as to cause precipitation of MgCl₂, and recovering same.

For example, the processes can further comprise calcining MgCl₂ into MgO and optionally recycling HCl so-produced.

For example, the processes can further comprises, after recovery of the rare earth elements and/or rare metals, reacting the liquid with HCl, and substantially selectively precipitating Na₂SO₄. For example, Na₂SO₄ can be precipitated by reacting the liquid with H₂SO₄.

For example, the processes can further comprises, after recovery of the rare earth elements and/or rare metals, reacting the liquid with HCl, and substantially selectively precipitating K₂SO₄. For example, K₂SO₄ can be precipitated by adding H₂SO₄.

For example, the liquid can be concentrated to a concentrated liquid having an iron chloride concentration of at least 30% by weight; and then the iron chloride can be hydrolyzed at a temperature of about 155 to about 350° C. while maintaining a ferric chloride concentration at a level of at least 65% by weight, to generate a composition comprising a liquid and precipitated hematite; recovering the hematite; and reacting the liquid with HCl. For example, such processes can further comprises reacting the liquid with H₂SO₄ so as to substantially selectively precipitate Na₂SO₄. The processes can also comprise further reacting the liquid with H₂SO₄ so as to substantially selectively precipitating K₂SO₄.

For example, the processes can comprise reacting dry individual salts (for example Na or K salts) obtained during the processes with H₂SO₄ and recovering HCl while producing marketable K₂SO₄ and Na₂SO₄ and recovering hydrochloric acid of about 15 to about 90% wt.

For example, sodium chloride produced in the processes can undergo a chemical reaction with sulfuric acid so as to obtain sodium sulfate and regenerate hydrochloric acid. Potassium chloride can undergo a chemical reaction with sulfuric acid so as to obtain potassium sulfate and regenerate hydrochloric acid. Sodium and potassium chloride brine solution can alternatively be the feed material to adapted small chlor-alkali electrolysis cells. In this latter case, common bases (NaOH and KOH) and bleach (NaOCl and KOCl) are produced.

For example, the processes can further comprise, after recovery of the rare earth elements and/or rare metals, recovering NaCl from the liquid, reacting the NaCl with H₂SO₄, and substantially selectively precipitating Na₂SO₄.

For example, the processes can further comprise, downstream of recovery of the rare earth elements and/or rare metals, recovering KCl from the liquid, reacting the KCl with H₂SO₄, and substantially selectively precipitating K₂SO₄.

For example, the processes can further comprise, downstream of recovery of the rare earth elements and/or rare metals, recovering NaCl from the liquid, carrying out an electrolysis to generate NaOH and NaOCl.

For example, the processes can further comprise, downstream of recovery of the rare earth elements and/or rare metals, recovering KCl from the liquid, reacting the KCl, carrying out an electrolysis to generate KOH and KOCl.

For example, the liquid can be concentrated to a concentrated liquid having a concentration of the at least one iron chloride of at least 30% by weight; and then the at least one iron chloride is hydrolyzed at a temperature of about 155 to about 350° C. while maintaining a ferric chloride concentration at a level of at least 65% by weight, to generate a composition comprising a liquid and precipitated hematite; recovering the hematite; and extracting NaCl and/or KCl from the liquid.

For example, the processes can further comprise reacting the NaCl with H₂SO₄ so as to substantially selectively precipitate Na₂SO₄.

For example, the processes can further comprise reacting the KCl with H₂SO₄ so as to substantially selectively precipitate K₂SO₄.

For example, the processes can further comprise carrying out an electrolysis of the NaCl to generate NaOH and NaOCl.

For example, the processes can further comprise carrying out an electrolysis of the KCl to generate KOH and KOCl.

For example, the processes can comprise separating the solid from the leachate and washing the solid so as to obtain silica having a purity of at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.5% or at least 99.9%.

For example, AlCl₃ can be in the form of AlCl₃.6H₂O.

For example, the processes can comprise reacting the leachate with gaseous HCl so as to obtain the liquid and the precipitate comprising the aluminum ions in the form of AlCl₃.6H₂O.

For example, the processes can comprise reacting the leachate with dry gaseous HCl so as to obtain the liquid and the precipitate comprising the aluminum ions in the form of AlCl₃.6H₂O.

For example, the processes can comprise reacting the leachate with acid of at least 30% wt. that was recovered, regenerated and/or purified as indicated in the present disclosure so as to obtain the liquid and the precipitate comprising the aluminum ions in the form of AlCl₃.6H₂O.

For example, the processes can comprise reacting the leachate with gaseous HCl so as to obtain the liquid and the precipitate comprising the aluminum ions, the precipitate being formed by crystallization of AlCl₃.6H₂O.

For example, the processes can comprise reacting the leachate with dry gaseous HCl so as to obtain the liquid and the precipitate comprising the aluminum ions, the precipitate being formed by crystallization of AlCl₃.6H₂O.

For example, aluminum ions can be precipitated under the form of AlCl₃ (for example AlCl₃.6H₂O) in a crystallizer, for example, by adding HCl having a concentration of about 26 to about 32 wt % or about 24 to about 26% wt.

For example, the gaseous HCl can have a HCl concentration of at least 85% wt. or at least 90% wt.

For example, the gaseous HCl can have a HCl concentration of about 90% wt. or about 90% to about 95% wt.

For example, during the crystallization of AlCl₃.6H₂O, the liquid can be maintained at a concentration of HCl of about 25 to about 35% by weight, about 30 to about 32% by weight or about 23 to about 26% by weight.

For example, the crystallization can be carried out at a temperature of about 45 to about 65° C. or about 50 to about 60° C.

For example, the HCl can be obtained from the gaseous HCl so-produced.

For example, in the processes of the present disclosure, a given batch or quantity of the aluminum-containing material will be leached, will then be converted into AlCl₃.6H₂O and when the HCl generated during calcination of AlCl₃.6H₂O into Al₂O₃ will be used for example to leach another given batch or quantity of the aluminum-containing material.

For example, the processes can comprise heating the precipitate at a temperature of at least 850, 900, 925, 930, 1000, 1100, 1200 or 1250° C. for converting AlCl₃.6H₂O into Al₂O₃.

For example, converting AlCl₃.6H₂O into Al₂O₃ can comprise calcination of AlCl₃.

For example, calcination is effective for converting AlCl₃.6H₂O into beta-Al₂O₃.

For example, calcination is effective for converting AlCl₃.6H₂O into alpha-Al₂O₃.

For example, converting AlCl₃.6H₂O into Al₂O₃ can comprise carrying out a calcination via a two-stage circulating fluid bed reactor or via a single stage circulating fluid bed, or via any arrangement fluid bed, kiln, or a plasma system.

For example, converting AlCl₃ into Al₂O₃ can comprise carrying out a calcination via a two-stage circulating fluid bed reactor that comprises a preheating system.

For example, converting AlCl₃.6H₂O into Al₂O₃ can comprise carrying out a calcination at low temperature, for example, of at least about 350° C., at least 375° C. about 300 to about 600° C., about 325 to about 550° C., about 350 to about 500° C., about 375 to about 450° C., about 375 to about 425° C., or about 385 to about 400° C. and/or injecting steam.

For example, converting AlCl₃.6H₂O into Al₂O₃ can comprise carrying out a calcination at low temperature, for example, at least 350° C. and/or injecting steam.

For example, converting AlCl₃.6H₂O into Al₂O₃ can comprise carrying out a calcination at low temperature, for example, less than 600° C. and/or injecting steam.

For example, converting AlCl₃.6H₂O into Al₂O₃ can comprise carrying out a calcination by using coal as combustion source and by using a degasification unit.

For example, steam (or water vapor) can be injected at a pressure of about 200 to about 700 psig, about 300 to about 700 psig, about 400 to about 700 psig, about 550 to about 650 psig, about 575 to about 625 psig, or about 590 to about 610 psig.

For example, steam (or water vapor) can be injected and a plasma torch can be used for carrying fluidization.

For example, the steam (or water vapor) can be overheated.

For example, the steam (or water vapor) can be at a temperature of about 300 to about 400° C.

For example, acid from the offgases generated during calcination can be then treated via a gas phase purification process.

For example, converting AlCl₃.6H₂O into Al₂O₃ can comprise carrying out a calcination by means of carbon monoxide (CO).

For example, converting AlCl₃.6H₂O into Al₂O₃ can comprise carrying out a calcination by means of a Refinery Fuel Gas (RFG).

For example, calcination can be carried out by injecting water vapor or steam and/or by using a combustion source chosen from fossil fuels, carbon monoxide, a Refinery Fuel Gas, coal, or chlorinated gases and/or solvents.

For example, the processes can comprise converting AlCl₃.6H₂O into Al₂O₃ by carrying out a calcination of AlCl₃.6H₂O that is provided by the combustion of gas mixture that is a an incoming smelter gas or a reducer offgas.

For example, the processes can comprise converting AlCl₃.6H₂O into Al₂O₃ by carrying out a calcination of AlCl₃.6H₂O that is provided by the combustion of gas mixture that is a an incoming smelter gas or a reducer offgas.

For example, the processes can comprise converting AlCl₃.6H₂O into Al₂O₃ by carrying out a calcination of AlCl₃.6H₂O that is provided by the combustion of gas mixture that comprises:

CH₄: 0 to about 1% vol;

C₂H₆: 0 to about 2% vol;

C₃H₈: 0 to about 2% vol;

C₄H₁₀: 0 to about 1% vol;

N₂: 0 to about 0.5% vol;

H₂: about 0.25 to about 15.1% vol;

CO: about 70 to about 82.5% vol; and

CO₂: about 1.0 to about 3.5% vol.

For example, O₂ can be substantially absent from the mixture.

For example, calcination can be carried out by injecting water vapor or steam and/or by using a combustion source chosen from natural gas or propane.

For example, calcination can be carried out by providing heat by means of electric heating, gas heating, microwave heating and plasma heating.

The obtained alumina can be washed by demineralized water so as to at least partially remove NaCl and/or KCl.

For example, the fluid bed reactor can comprise a metal catalyst chosen from metal chlorides.

For example, the fluid bed reactor can comprise a metal catalyst that is FeCl₃, FeCl₂ or a mixture thereof.

For example, the fluid bed reactor can comprise a metal catalyst that is FeCl₃.

For example, the preheating system can comprise a plasma torch.

For example, steam can be used as the fluidization medium heating. Heating can also be electrical.

For example, a plasma torch can be used for preheating the calcination reactor.

For example, a plasma torch can be used for preheating air entering in the calcination reactor.

For example, a plasma torch can be used for preheating a fluid bed.

For example, the plasma torch can be effective for generating steam that is injected into a calcination reactor.

For example, the plasma torch can be effective for generating steam that is as fluidization medium in a fluid bed reactor.

For example, the calcination medium can be substantially neutral in terms of O₂ (or oxidation). For example, the calcination medium can favorize reduction (for example a concentration of CO of about 100 ppm).

For example, the calcination medium is effective for preventing formation of Cl₂.

For example, the processes can comprise converting AlCl₃.6H₂O into Al₂O₃ by carrying out a calcination of AlCl₃.6H₂O that is provided by the combustion of gas mixture that comprises:

CH₄: 0 to about 1% vol;

C₂H₆: 0 to about 2% vol;

C₃H₈: 0 to about 2% vol;

C₄H₁₀: 0 to about 1% vol;

N₂: 0 to about 0.5% vol;

H₂: about 0.25 to about 15.1% vol;

CO: about 70 to about 82.5% vol; and

CO₂: about 1.0 to about 3.5% vol.

Such a mixture can be efficient for reduction in off gas volume of 15.3 to 16.3%; therefore the capacity increases of 15.3 to 16.3% proven on practical operation of the circulating fluid bed. Thus for a same flow it represents an Opex of 0.65*16.3%=10.6%.

For example, the air to natural gas ratio of (Nm³/h over Nm³/h) in the fluid bed can be about 9.5 to about 10

For example, the air to CO gas ratio of (Nm³/h over Nm³/h) in the fluid bed can be about 2 to about 3.

For example, the processes can comprise, before leaching the aluminum-containing material, a pre-leaching removal of fluorine optionally contained in the aluminum-containing material.

For example, the processes can comprise leaching of the aluminum-containing material with HCl so as to obtain the leachate comprising aluminum ions and the solid, separating the solid from the leachate; and further treating the solid so as to separate SiO₂ from TiO₂ that are contained therein.

For example, the processes can comprise leaching the aluminum-containing material with HCl so as to obtain the leachate comprising aluminum ions and the solid, separating the solid from the leachate; and further treating the solid with HCl so as to separate Si from Ti that are contained therein.

For example, the processes can comprise leaching the aluminum-containing material with HCl so as to obtain the leachate comprising aluminum ions and the solid, separating the solid from the leachate; and further treating the solid with HCl at a concentration of less than 20% wt., at a temperature of less than 85° C., in the presence of MgCl₂, so as to separate Si from Ti that are contained therein.

For example, the processes can comprise leaching said fly ash with HCl so as to obtain the leachate comprising aluminum ions and the solid, separating the solid from the leachate; and further treating the solid so as to separate SiO₂ from TiO₂ that are contained therein.

For example, the processes can comprise comprising leaching the fly ash with HCl so as to obtain the leachate comprising aluminum ions and the solid, separating the solid from the leachate; and further treating the solid with HCl so as to separate SiO₂ from TiO₂ that are contained therein.

For example, the processes can comprise leaching the fly ash with HCl so as to obtain the leachate comprising aluminum ions and the solid, separating the solid from the leachate; and further treating the solid with HCl at a concentration of less than 20% by weight, at a temperature of less than 85° C., in the presence of MgCl, so as to separate SiO₂ from TiO₂ that are contained therein.

For example, converting AlCl₃.6H₂O into Al₂O₃ can comprise carrying out a one-step calcination.

For example, the processes can comprise converting AlCl₃.6H₂O into Al₂O₃ by carrying out a calcination of AlCl₃.6H₂O, the calcination comprising steam injection.

For example, calcination can be carried out at different temperatures with steam. Temperature applied of superheated steam can be of about 350° C. to about 550° C. or about 350° C. to about 940° C. or about 350° C. to about 1200° C.

For example, multi stage evaporation step of the hydrolyser can be carried out to reduce drastically energy consumption.

For example, the processes can be effective for providing an Al₂O₃ recovery yield of at least 93%, at least 94%, at least 95%, about 90 to about 95%, about 92 to about 95%, or about 93 to about 95%.

For example, the processes can be effective for providing a Fe₂O₃ recovery yield of at least 98%, at least 99%, about 98 to about 99.5%, or about 98.5 to about 99.5%.

For example, the processes can be effective for providing a MgO recovery yield of at least 96%, at least 97%, at least 98%, or about 96 to about 98%.

For example, the processes can be effective for providing a HCl recovery yield of at least 98%, at least 99%, about 98 to about 99.9% or about 98 to about 99.99%.

For example, the processes can be effective for providing chlorides of rare earth elements (REE-Cl) and chlorides of rare metals (RM-Cl) in recovery yields of about 75% to about 96.5% by using internal processes via an internal concentration loop.

For example, the processes can be effective for providing hydrochloric acid recovery yield of about 99.75% with non-hydrolysable elements.

For example, the aluminum-containing material can be argillite.

For example, the aluminum-containing material can be bauxite.

For example, the aluminum-containing material can be red mud.

For example, the aluminum-containing material can be fly ash.

For example, the aluminum-containing material can be chosen from industrial refractory materials.

For example, the aluminum-containing material chosen from aluminosilicate minerals.

For example, the processes can be effective for avoiding producing red mud.

For example, the alumina and the other products are substantially free of red mud.

For example, HCl can be recycled. For example, such a recycled HCl can be concentrated and/or purified.

For example, gaseous HCl can be concentrated and/or purified by means of H₂SO₄. For example, gaseous HCl can be treated with H₂SO₄ so as to reduce the amount of water present in the gaseous HCl. For example, gaseous HCl can be passed through a packed column where it is contacted with a H₂SO₄ countercurrent flow. For example, by doing so, concentration of HCl can be increased by at least 50% wt., at least 60% wt., at least 70% wt., at least 75% wt., at least 80% wt., about 50% wt. to about 80% wt., about 55% wt. to about 75% wt., or about 60% wt. For example, the column can be packed with a polymer such as polypropylene (PP) or polytrimethylene terephthalate (PTT).

For example, gaseous HCl can be concentrated and/or purified by means of CaCl₂ or LiCl. For example, gaseous HCl can be passed through a column packed with CaCl₂ or LiCl.

For example, the concentration of gaseous HCl can be increased from a value below the azeotropic point before treatment to a value above the azeotropic point after treatment.

For example, the various products obtained by the processes of the present disclosure such as alumina, hematite, titanium oxides, magnesium oxides, rare earth elements and rare metals can be further purified by means of a plasma torch. For example, the rare earth elements and rare metals, once isolated, can be individually injected into a plasma torch so as to further purify them.

For example, the acid can be chosen from HCl, HNO₃, H₂SO₄ and mixtures thereof.

For example, the first metal can be aluminum or iron. For example, the second metal can be aluminum or iron.

For example, when the first metal is aluminum, the aluminum ions can be removed from said leachate by reacting the leachate with an acid (such as HCl) so as to obtain a liquid and a precipitate comprising said aluminum ions (for example in the form of AlCl₃), and separating said precipitate from said liquid. Then, iron ions can be recovered from the liquid by precipitation, hydrolysis, purification etc.

For example, when the first metal is iron, the iron ions can be removed from said leachate by leachate with a base (such as NaOH or KOH) so as to obtain a liquid and a precipitate comprising said iron ions, and separating said precipitate from said liquid. Then, aluminum ions can be recovered from the liquid by precipitation, hydrolysis, purification etc.

For example, the processes can comprise precipitating said Al³⁺ ions under the form of Al(OH)₃. For example, wherein precipitating said Al³⁺ under the form of Al(OH)₃ is carried out at a pH of about 7 to about 10, about 9 to about 10, about 9.2 to about 9.8, about 9.3 to about 9.7, about 9.5, about 7.5 to about 8.5, about 7.8 to about 8.2 or about 8.

For example, the iron ions can be precipitated at a pH greater than 11, a pH greater than 12, a pH comprised between 10 and 11, a pH of about 11.5 to about 12.5 or of about 11.8 to about 12.0.

For example, the iron ions can be precipitated at a pH of about 3.0 to about 5.5, about 3 to about 5, about 3 to about 4, about 3.0 to about 3.5, about 3.5 to about 4.0, about 4 to about 5, about 4.5 to about 5.0, about 5 to about 6 by adding said base.

For example, when the first metal to be removed is iron, the processes can be carried out in a manner similar as described in WO2008/141423 or in WO2012/065253 and by using, for example, using an aluminum-containing material as described in the present disclosure as starting material. These document are hereby integrated by reference in their entirety.

For example, the Al³⁺ ions can be purified.

For example, the processes can further comprise converting alumina (Al₂O₃) into aluminum. Conversion of alumina into aluminum can be carried out, for example, by using the Hall-Héroult process. References is made to such a well known process in various patents and patent applications such as US 20100065435; US 20020056650; U.S. Pat. Nos. 5,876,584; 6,565,733. Conversion can also be carried out by means of other methods such as those described in U.S. Pat. Nos. 7,867,373; 4,265,716; 6,565,733 (converting alumina into aluminum sulfide followed by the conversion of aluminum sulfide into aluminum.). For example, aluminium can be produced by using a reduction environment and carbon at temperature below 200° C. Aluminum can also be produced by reduction using potassium and anhydrous aluminum chloride Wohler Process).

For example, converting AlCl₃ into Al₂O₃ can be done under an inert gas atmosphere.

For example, converting AlCl₃ into Al₂O₃ can be done under a nitrogen atmosphere.

For examples, the processes of the present disclosure can be continuous processes or semi-continuous processes.

According to one example as shown in FIG. 1, the processes can involve the following steps (the reference numbers in FIG. 1 correspond to the following steps):

1—The aluminum-containing material is reduced to an average particle size of about 50 to about 80 μm.

2—The reduced and classified material is treated with hydrochloric acid which allows for dissolving, under a predetermined temperature and pressure, the aluminum with other elements like iron, magnesium and other metals including rare earth elements and/or rare metals. The silica and titanium (if present in raw material) remain totally undissolved.

3—The mother liquor from the leaching step then undergoes a separation, a cleaning stage in order to separate the purified silica from the metal chloride in solution. The purified silica can then optionally undergo one or two additional leaching stages (for example at a temperature of about 150 to about 160° C.) so as to increase the purity of silica above 99.9%. TiO₂ contained in silica can be separated from silica through a leach made by using HCl and MgCl₂ as a lixiviant composition.

4—The spent acid (leachate) obtained from step 1 is then brought up in concentration with dry and highly concentrated gaseous hydrogen chloride by sparging this one into a crystallizer. This results into the crystallization of aluminum chloride hexahydrate (precipitate) with a minimum of other impurities. Depending on the concentration of iron chloride at this stage, further crystallization step(s) can be required. The precipitate is then separated from the liquid.

5—The aluminum chloride hexahydrate is then calcined (for example by means of a rotary kiln, fluid bed, etc) at high temperature in order to obtain the alumina form. Highly concentrated gaseous hydrogen chloride is then recovered and excess is brought in aqueous form to the highest concentration possible so as to be used (recycled) in the acid leaching step. Acid can also be directly sent in gas phase to the acid purification stage to increase HCl concentration from about 30 wt % to about 95 wt %. This can be done, for example, during drying stage.

6—Iron chloride (the liquid obtained from step 4) is then pre-concentrated and hydrolyzed at low temperature in view of the Fe₂O₃ (hematite form) extraction and acid recovery from its hydrolysis. All heat recovery from the calcination step (step 5), the leaching part exothermic reaction (step 1) and other section of the processes is being recovered into the pre-concentrator.

10—After the removal of hematite, a solution rich in rare earth elements and/or rare metals can be processed. As it can be seen in FIG. 3, an internal recirculation can be done (after the removal of hematite) and the solution rich in rare earth elements and/or rare metals can be used for crystallization stage 4. Extraction of the rare earth elements and/or rare metals can be done as described in PCT/CA2012/000253 and/or PCT/CA2012000419. These two documents are hereby integrated by reference in their entirety.

Other non-hydrolysable metal chlorides (Me—Cl) such as MgCl₂ and others then undergo the following steps:

7—The solution rich in magnesium chloride and other non-hydrolysable products at low temperature is then brought up in concentration with dry and highly concentrated gaseous hydrogen chloride by sparging it into a crystallizer. This results into the precipitation of magnesium chloride as an hexahydrate, for example after sodium and potassium chloride removal.

8—Magnesium chloride hexahydrate is then calcined (either through a rotary kiln, fluid bed, etc.) and hydrochloric acid at very high concentration is thus regenerated and brought back to the leaching step.

9—Other Me—Cl undergo a standard pyrohydrolysis step where mixed oxides (Me—O) can be produced and hydrochloric acid at the azeotropic point (20.2% wt.) is regenerated.

NaCl can undergo chemical reaction with H₂SO₄ to produce Na₂SO₄ and HCl at a concentration at or above azeotropic concentration. Moreover, KCl can undergo chemical reaction with H₂SO₄ to produce K₂SO₄ and HCl having a concentration that is above the azeotropic concentration. Sodium and potassium chloride brine solution can be the feed material to adapted small chlor-alkali electrolysis cells. In this latter case, common bases (NaOH and KOH) and bleach (NaOCl and KOCl) are produced as well as HCl.

For example, the liquid can be concentrated to a concentrated liquid having an iron chloride concentration of at least 30% by weight; and then the iron chloride can be hydrolyzed at a temperature of about 155 to about 350° C. while maintaining a ferric chloride concentration at a level of at least 65% by weight, to generate a composition comprising a liquid and precipitated hematite, and recovering the hematite.

For example, the liquid can be concentrated to a concentrated liquid having an iron chloride concentration of at least 30% by weight; and then the iron chloride can be hydrolyzed at a temperature of about 155 to about 350° C. while maintaining a ferric chloride concentration at a level of at least 65% by weight, to generate a composition comprising a liquid and precipitated hematite; recovering the hematite; and recovering rare earth elements and/or rare metals from the liquid. For example, the processes can further comprise, after recovery of the rare earth elements and/or rare metals, reacting the liquid with HCl so as to cause precipitation of MgCl₂, and recovering same.

However, the person skilled in the art will understand that the continuous processes can handle high percentages of silica (>55%) and impurities as well as relatively low percentages of aluminum (for example as low as about 15%) and still being economically and technically viable. Satisfactory yields can be obtained (>93-95%) on Al₂O₃ and greater than 75%, 85 or 90% on rare earth elements and/or rare metals. No pre-thermal treatment in most cases are required. The processes disclosed in the present disclosure involve special techniques on leaching and acid recovery at very high strength, thereby offering several advantages over alkaline processes.

In step 1 the mineral, whether or not thermally treated is crushed, milled, dried and classified to have an average particle size of about 50 to about 80 μm.

In step 2, the milled raw material is introduced into the reactor and will undergo the leaching phase.

The leaching hydrochloric acid used in step 2 can be a recycled or regenerated acid from steps 5, 6, 8, 9, 10 and 11 (see FIG. 3) its concentration can vary from 15% to 45% weight percent. Higher concentration can be obtained using membrane separation, cryogenic and/or high pressure approach. The acid leaching can be carried out under pressure and at temperature close to its boiling point thus, allowing a minimal digestion time and extended reaction extent (90%-100%). Leaching (step 2) can be accomplished in a semi-continuous mode where spent acid with residual free hydrochloric acid is replaced, following pressurization, by highly concentrated acid at a certain stage of the reaction or allowing a reduced acid/mineral ratio, thereby reducing reaction time and improving reaction kinetics. For example, kinetic constant k can be: 0.5-0.75 g/mole·L, or 0.65-0.82 g/mole·L.

As previously indicated, alkali metals, iron, magnesium, sodium, calcium, potassium, rare earth elements and other elements will also be in a chloride form at different stages. Silica and optionally titanium can remain undissolved and will undergo (step 3) a liquid/solid separation and cleaning stage. The processes of the present disclosure tend to recover maximum amount of free hydrochloric acid left and chlorides in solution in order to maximize hydrochloric acid recovery yield, using techniques such as rake classifying, filtration with band filters, centrifugation, and others. Pure SiO₂ (one additional leaching stage) cleaning with nano water purity 99% min. Mother liquor free of silica is then named as spent acid (various metal chlorides and water) and goes to the crystallization step (step 4).

In step 4, the spent acid (or leachate) with a substantial amount of aluminum chloride is then saturated with dry and highly concentrated gaseous hydrogen chloride obtained or recycled from step 5 or with aqueous HCl>30% wt., which results in the precipitate of aluminum chloride hexahydrate (AlCl₃.6H₂O). The precipitate retained is then washed and filtered or centrifuged before being fed to the calcination stage (step 5). The remaining of the spent acid from step 4 is then processed to acid recovery system (steps 6 to 8) where pure secondary products will be obtained.

In step 5, aluminum oxide (alumina) is directly obtained from high temperature conditions. The highly concentrated hydrogen chloride in gaseous form obtained can be fed to steps 4 and 7 for crystallization where it can be treated through hydrophobic membranes. The excess hydrogen chloride is absorbed and used as regenerated acid to the leaching step 2 as highly concentrated acid, higher than the concentration at the azeotropic point (>20.2%). For example, such a concentration can be about 18 to about 45 weight %, about 25 to about 45 weight % or between 25 and 36 weight %. Acid can also be redirected in gas phase directly (>30 wt %) to acid purification.

After step 4, various chlorides derivatives (mainly iron with magnesium and rare earth elements and rare metals) are next subjected to an iron extraction step. Such a step can be carried out for example by using the technology disclosed in WO 2009/153321, which is hereby incorporated by reference in its entirety. Moreover, hematite can be seeded for crystal growth. For example, hematite seeding can comprise recirculating the seeding.

In step 6, a hydrolysis at low temperature (155-350° C.) is carried out and pure Fe₂O₃ (hematite) is being produced and hydrochloric acid of at least 15% concentration is being regenerated. The method as described in WO 2009/153321 is processing the solution of ferrous chloride and ferric chloride, possible mixtures thereof, and free hydrochloric acid through a series of steps pre-concentration step, oxidation step where ferrous chloride is oxidized into ferric form, and finally through an hydrolysis step into an operational unit called hydrolyser where the ferric chloride concentration is maintained at 65 weight % to generate a rich gas stream where concentration ensures a hydrogen chloride concentration of 15-20.2% and a pure hematite that will undergo a physical separation step. Latent heat of condensation is recovered to the pre-concentration and used as the heating input with excess heat from the calcination stage (step 5).

The mother liquor from the hydrolyser (step 6) can be recirculated partially to first step crystallization process where an increase in concentration of non-hydrolysable elements is observed. After iron removal, the liquor is rich in other non-hydrolysable elements and mainly comprises magnesium chloride or possible mixture of other elements (various chlorides) and rare earth elements and rare metals.

Rare earth elements and rare metals in form of chlorides are highly concentrated in percentage into the hydrolyser operational unit (step 6) and are extracted from the mother liquor (step 10) where various known techniques can be employed to extract a series of individual RE-O (rare earth oxides). Among others, the processes of the present disclosure allows to concentrate to high concentration the following elements, within the hydrolyser: scandium (Sc), galium (Ga), yttrium (Y), dysperosium (Dy), cerium (Ce), praseodynium (Pr), neodynium (Nd), europium (Eu), lanthanum (La), samarium (Sm), gadolinium, (Gd), erbium (Er), zirconium (Zr) and mixtures of thereof. Technologies that can be used for extracting rare earth elements and/or rare metals can be found, for example, in Zhou et al. in RARE METALS, Vol. 27, No. 3, 2008, p 223-227, and in US 2004/0042945, hereby incorporated by reference in their entirety. The person skilled in the art will also understand that various other processes normally used for extracting rare earth elements and/or rare metals from the Bayer process can also be used. For example, various solvent extraction techniques can be used. For certain elements, a technique involving octylphenyl acid phosphate (OPAP) and toluene can be used. HCl can be used as a stripping agent. This can be effective for recovering Ce₂O₃, Sc₂O₃, Er₂O₃ etc. For example, different sequence using oxalic acid and metallic iron for ferric chloride separation can be used.

The spent acid liquor from steps 6 and 10 rich in value added metals, mainly magnesium, is processed to step 7. The solution is saturated with dry and highly concentrated gaseous hydrogen chloride from step 5, which results in the precipitation of magnesium chloride hexahydrate. For example, same can be accomplished with HCl in aqueous form over 30% wt. The precipitate retained, is fed to a calcination stage step 8 where pure MgO (>98% wt.) is obtained and highly concentrated hydrochloric acid (for example of at least 38%) is regenerated and diverted to the leaching step (step 2). An alternative route for step 7 is using dry gaseous hydrochloric acid from step 8.

In step 9, metal chlorides unconverted are processed to a pyrohydrolysis step (700-900° C.) to generate mixed oxides and where hydrochloric acid from 15-20.2% wt. concentration can be recovered.

According to another example as shown in FIG. 3, the processes can be similar to the example shown in FIG. 1 but can comprise some variants as below discussed.

In fact, as shown in FIG. 3, the processes can comprise (after step 6 or just before step 10) an internal recirculation back to the crystallization step 4. In such a case. The mother liquor from the hydrolyser (step 6) can be recirculated fully or partially to the crystallization of step 4 where a concentration increase will occur with respect to the non-hydrolysable elements including rare earth elements and/or rare metals.

Such a step can be useful for significantly increasing the concentration of rare earth elements and/or rare metals, thereby facilitating their extraction in step 10.

With respect to step 7, the solution rich in magnesium chloride and other non-hydrolysable products at low temperature is, as previously discussed, then brought up in concentration with dry and highly concentrated gaseous hydrogen chloride by sparging it into a crystallizer. This can result into the precipitation of magnesium chloride as an hexahydrate (for example after sodium and potassium chloride removal). This can also be accomplished with HCl in aqueous form.

As shown in FIG. 3, an extra step 11 can be added. Sodium chloride can undergo a chemical reaction with sulfuric acid so as to obtain sodium sulfate and regenerate hydrochloric acid at a concentration at or above the azeotropic point. Potassium chloride can undergo a chemical reaction with sulfuric acid so as to obtain potassium sulfate and regenerate hydrochloric acid at a concentration above the azeotropic concentration. Sodium and potassium chloride brine solution can be the feed material to adapted small chlor-alkali electrolysis cells. In this latter case, common bases (NaOH and KOH) and bleach (NaOCl and KOCl) are produced and can be reused to some extent in other areas of the processes of the present disclosure (scrubber, etc.).

The following are non-limitative examples.

EXAMPLE 1 Preparation of Alumina and Various Other Products

As a starting material a sample of clay was obtained from the Grande Vallée area in Québec, Canada.

These results represent an average of 80 tests carried out from samples of about 900 kg each.

Crude clay in the freshly mined state after grinding and classification had the following composition:

-   Al₂O₃: 15%-26%; -   SiO₂: 45%-50%; -   Fe₂O₃: 8%-9%; -   MgO: 1%-2%; -   Rare earth elements and/or rare metals: 0.04%-0.07%; -   LOI: 5%-10%.

This material is thereafter leached in a two-stage procedure at 140-170° C. with 18-32 weight % HCl. The HCl solution was used in a stoichiometric excess of 10-20% based on the stoichiometric quantity required for the removal of the acid leachable constituents of the clay. In the first leaching stage of the semi-continuous operation (step 2), the clay was contacted for 2.5 hours with required amount or certain proportion of the total amount of hydrochloric acid. After removal of the spent acid, the clay was contacted again with a minimum 18 weight % hydrochloric acid solution for about 1.5 hour at same temperature and pressure.

A typical extraction curve obtained for both iron and aluminum for a single stage leaching is shown in FIG. 2.

The leachate was filtered and the solid was washed with water and analyzed using conventional analysis techniques (see step 3 of FIG. 1). Purity of obtained silica was of 95.4% and it was free of any chlorides and of HCl.

In another example, the purity of the silica was 99.67% through an extra leaching step.

After the leaching and silica removal, the concentration of the various metal chlorides was:

-   AlCl₃: 15-20%; -   FeCl₂: 4-6%; -   FeCl₃: 0.5-2.0%; -   MgCl₂: 0.5-2.0%; -   REE-Cl: 0.1-2% -   Free HCl: 5-50 g/l

Spent acid was then crystallized using about 90 to about 98% pure dry hydrochloric acid in gas phase in two stages with less than 25 ppm iron in the aluminum chloride hexahydrate formed. The concentration of HCl in solution (aqueous phase) was about 22 to about 32% or 25 to about 32%, allowing 95.3% of Al₂O₃ recovery. The recovered crystallized material (hydrate form of AlCl₃ having a minimum purity of 99.8%) was then calcined at 930° C. or 1250° C., thus obtaining the α form of the alumina. Heating at 930° C. allows for obtaining the beta-form of alumina while heating at 1250° C. allows for obtaining the alpha-form.

Another example was carried out at low temperature (decomposition and calcination at about 350° C.) and the α form of the alumina was less than 2%.

HCl concentration in gas phase exiting the calcination stage was having a concentration greater than 30% and was used (recycled) for crystallization of the AlCl₃ and MgCl₂. Excess of hydrochloric acid is absorbed at the required and targeted concentration for the leaching steps.

Iron chloride (about 90 to about 99.5%% in ferric form) is then sent to a hydrothermal process in view of its extraction as pure hematite (Fe₂O₃). This can be done by using the technology described in WO 2009/153321 of low temperature hydrolysis with full heat recovery from calcining, pyrohydrolysis and leaching stage.

Rare earth elements and rare metals are extracted from the mother liquor of the hydrolyzer where silica, aluminum, iron and a great portion of water have been removed and following preconcentration from hydrolyser to crystallization. It was measured that rare earth elements can be concentrated by a factor of about 4.0 to 10.0 on average within the hydrolyzer itself on a single pass through it i.e. without concentration loop. The following concentration factors have been noted within the hydrolyzer (single pass):

Ce>6

La>9

Nd>7

Y>9

Remaining magnesium chloride is sparged with dry and highly concentrated hydrochloric acid and then calcinated to MgO while recovering high concentration acid (for example up to 38.4%).

Mixed oxides (Me—O) containing other non-hydrolysable components were then undergoing a pyrohydrolysis reaction at 700-800° C. and recovered acid (15-20.2% wt.) was rerouted for example to the leaching system.

Overall Yields Obtained:

-   Al₂O₃: 93.0-95.03% recovery; -   Fe₂O₃: 92.65-99.5% recovery; -   Rare earth elements: 95% minimum recovery (mixture); -   MgO: 92.64-98.00% recovery; -   Material discarded: 0-5% maximum; -   HCl global recovery: 99.75% minimum; -   HCl strength as feed to leaching 15-32% (aqueous); 95% (gas) -   Red mud production: none.

EXAMPLE 2 Preparation of Alumina and Various Other Products

A similar feed material (bauxite instead of clay) was processed as per in example 1 up to the leaching stage and revealed to be easily leachable under the conditions established in example 1. It provided an extraction percentage of 100% for the iron and over 90-95% for aluminum. The technology was found to be economically viable and no harmful by-products (red mud) were generated. Samples tested had various concentrations of Al₂O₃ (up to 51%), Fe₂O₃ (up to 27%) and MgO (up to 1.5%). Gallium extraction of 97.0% was measured. Scandium extraction was 95%.

EXAMPLE 3 HCl Gas Enrichment and Purification: H₂SO₄ Route

H₂SO₄ can be used for carrying out purification of HCl. It can be carried out by using a packing column with H₂SO₄ flowing counter currently (see FIG. 4). This allows for converting the recovered HCl into HCl having a concentration above the azeotropic point (20.1% wt) and increase its concentration by about 60 to about 70% at minimum.

Water is absorbed by H₂SO₄ and then H₂SO₄ regeneration is applied where H₂SO₄ is brought back to a concentration of about 95 to about 98% wt. Water release at this stage free of sulphur is recycled back and used for crystallization dissolution, etc. Packing of the column can comprise polypropylene or polytrimethylene terephthalate (PTT).

Combustion energy can be performed with off gas preheating air and oxygen enrichment. Oxygen enrichment: +2% represents flame temperature increase by: 400° C. maximum.

EXAMPLE 4 HCl Gas Enrichment and Purification: Calcium Chloride to Calcium Chloride Hexahydrate (Absorption/Desorption Process)

As shown in FIG. 5, CaCl₂ can be used for drying HCl. In fact, CaCl₂ can be used for absorbing water contained into HCl. In such a case, CaCl₂ is converted into its hexachloride form (CaCl₂.6H₂O) and one saturated system is eventually switched into regeneration mode where hot air recovered from calcination off gas of alumina and magnesium oxide spray roasting is introduced to regenerate the fixed bed. Alternatively, other absorbing agent such as LiCl can be used instead of CaCl₂. Such an ion/exchange type process can be seen in FIG. 4 and the cycle can be inversed to switch from one column to another one.

The person skilled in the art would understand that the processes described in examples 3 and 4 can be used in various different manners. For example, these processes can be combined with the various processes presented in the present disclosure. For example, such purifications techniques can be integrated to the processes shown in FIG. 1, 3 or 6. For example, these techniques can be used downstream of at least one of step chosen from steps 5, 6, 8, 9, 10 and 11 (see FIGS. 1 and 3). They can also be used downstream of step 4 and/or step 7. They can also be used downstream of at least one of step chosen from steps 104 to 111 (see FIG. 6)

EXAMPLE 5 Preparation of Alumina and Various Other Products

This example was carried out by using a process as represented in FIGS. 6 and 7. It should be noted that the processes represented in FIGS. 6 and 7 differ only by the fact that FIG. 7 show to additional stages i.e. stages 112 and 113.

Raw Material Preparation

Raw material, clay for example, was processed in a secondary crusher in the clay preparation plant 101. Dry milling and classifying occurs on a dry basis in vertical roller mills (for example Fuller-Loesche LM 30.41). The clay preparation 101 included three roller mills; two running at a capacity of approximately 160-180 tph and one on standby. Raw material, if required, can be reduced to 85% less than 63 microns. Processed material was then stored in homogenization silos before being fed to the acid leaching plant 102. Below in Table 1 are shown results obtained during stage 101. If the ore contains the fluorine element, a special treatment can be applied before carrying out the 102 stage. In presence of hydrochloric acid, fluorine can produce hydrofluoric acid. This acid is extremely corrosive and damaging for human health. Thus, before leaching 102, an optional treatment fluorine separation 112 can be done. Stage 112 can comprise treating the processed material coming from stage 101 with an acid in a pre-leaching treatment so as to remove hydrofluoric acid. Therefore, depending on the composition of the raw material, a fluorine separation stage 112 (or pre-leaching stage 112) can be carried out.

TABLE 1 Clay preparation Rate 290 tph Composition feed SiO₂: 50.9% (main constituents) Al₂O₃: 24.0% Fe₂O₃: 8.51% CaO: 0.48% MgO: 1.33% Na₂O: 1.06% K₂O: 2.86% MnO: 0.16% Cr₂O₃: 0.01% TiO₂: 0.85% P₂O₅: 0.145%  SrO: 0.015%  BaO: 0.05% V₂O₅ 0.0321%  Other 9.63% (including H₂O and REE): Obtained particle size 85% <63 μm Residual moisture 0.5-0.7% Yield 99.5% min Acid Leaching

Next, acid leaching 102 was performed semi-continuously in an 80 m³ glass-lined reactor. Semi-continuous mode comprises replacing reacted acid ⅓ in the reaction period with higher concentration regenerated acid, which greatly improves reaction kinetics. The reactor arrangement comprises for example, a series of three reactors.

Leaching was performed at high temperature and pressure (about 160 to about 195° C. and pressures of about 5 to about 8 barg) for a fixed period of time. Reaction time was a function of the reaction extent targeted (98% for Al₂O₃), leaching mode, acid strength, and temperature/pressure applied.

Spent acid recovered out of the acid leaching 102 was then filtered 103 from unreacted silica and titanium dioxide and washed through an automated filter press where all free HCl and chloride are recovered. This allows, for example, a maximum quantity of about 30 ppm SiO₂ going into spent liquor. Cleaned silica at a concentration of ≈96%+SiO₂ is then produced. Various options are possible at that point. For example, the 96% silica can undergo final neutralization through caustic bath, cleaning, and then bricketing before storage. According to another example, the silica purified by adding another leaching step followed by a solid separation step that ensures TiO₂ removal (see stage 113 in FIG. 7). In that specific case, high purity silica 99.5%+ is produced. In stage 113, titanium and silicium can be separated from one another in various manners. For example, the solid obtained from stage 103 can be leached in the presence of MgCl₂ at a temperature below 90 or 80° C. and at low acid concentration. For example, acid concentration can be below 25 or 20%. The acid can be HCl or H₂SO₄. In such a case, titanium remains soluble after such a leaching while titanium is still in a solid form. These solid and liquid obtained after stage 113 are thus separated to provide eventually TiO₂ and SiO₂. Water input and flow for silica cleaning is in a ratio of 1:1 (silica/water) (150 t/h SiO₂/150 t/h H₂O), but comprises of wash water circulation in closed loop in the process and limited amount of process water for final cleaning of the silica and recovery of all chlorides and free HCl generated at the leaching stage. Below in Table 2 are shown results obtained during stage 102.

TABLE 2 Acid Leaching Equivalent solid feed rate 259.6 tph Operation mode Semi-continuous Acid to clay ratio 3.10 @ 23% wt (Equivalent to 3.35 with semi-continuous at 18.0% wt) Regenerated acid 18.0-32.0% concentration Operating temperature 150-155° C. (Pilot) 165-200° C. (Plant) MAWP 120 psig Typical chemical Fe₂O₃ + 6 HCl → 2 FeCl₃ + 3H₂O reactions Al₂O₃ + 6 HCl → 2 AlCl₃ + 3 H₂O MgO + 2 HCl → MgCl₂ + H₂O K₂O + 2 HCl → 2 KCl + H₂O Re₂O₃ + 6 HCl → 2 ReCl₃ + 3H₂O Spent acid flow to 600-1100 m³/h crystallization Practical chemical FeCl₃ 4.33% composition after step FeCl₂ 0.19% 102 without solid (SiO₂) AlCl₃ 16.6% MgCl₂ 0.82% NaCl  1.1% KCl  1.2% CaCl₂ 0.26% Extraction yields Iron  100% Al₂O₃   98% SiO₂ Recovery 99.997% AlCl₃ Crystallization

Spent acid, with an aluminum chloride content of about 20 to about 30%, was then processed in the crystallization stage 104. Dry and highly concentrated HCl (>90% wt.) in gas phase was sparged in a two-stage crystallization reactor, which allows the crystallization of aluminum chloride hexahydrate.

The flow rate of acid through these reactors is about 600 to about 675 m³/h and the reactor was maintained at about 50 to about 60° C. during this highly exothermic reaction. Heat was recovered and exchanged to the acid purification 107 part of the plant thus ensuring proper heat transfer and minimizing heat consumption of the plant. Aluminum chloride solubility decreases rapidly, compared to other elements, with the increase in concentration of free HCl in the crystallization reactor. The concentration of AlCl₃ for precipitation/crystallization was about 30%

The HCl concentration during crystallization was thus about 30 to about 32% wt.

The aqueous solution from the crystallization stage 104 was then submitted to the hydrothermal acid recovery plant 105, while the crystals are processed through the decomposition/calcination stage in the calcination plant 106.

A one-step crystallization stage or a multi-step crystallization stage can be done. For example, a two-steps crystallization stage can be carried out.

Below in Tables 3A and 3B are shown results obtained during stage 104.

TABLE 3A Aluminum chloride crystallization Number of crystallization 2 steps Operating temperature 50-60° C. Sparging HCl concentration 90% (gaseous) Typical chemicals formed AlCl₃•6H₂O (s) Metal chlorides (aq) AlCl₃•6H₂O residual <5% (practical); 8%

TABLE 3B Typical crystals composition main constituents obtained at pilot scale and feeding calcination Component Weight distribution (%) AlCl₃•6H₂O 99.978 BaCl₂•2H₂O 0.0000 CaCl₂•6H₂O 0.0009 CrCl₄ 0.0022 CuCl₂•2H₂O 0.0000 FeCl₃•6H₂O 0.0019 KCl 0.0063 MgCl₂•6H₂O 0.0093 MnCl₂•4H₂O 0.0011 NaCl 0.0021 SiCl₄ 0.0004 SrCl₂•6H₂O 0.0000 TiCl₄ 0.0001 VCl₄ 0.0000 Free Cl⁻ 0.0000 Calcination and Hydrothermal Acid Recovery

The calcination 106 comprises the use of a two-stage circulating fluid bed (CFB) with preheating systems. The preheating system can comprise a plasma torch to heat up steam to process. It processes crystals in the decomposition/calcination stage. The majority of the hydrochloric acid was released in the first stage which was operated at a temperature of about 350° C., while the second stage performs the calcination itself. Acid from both stages (about 66 to about 68% of the recovered acid from the processes) was then recovered and sent to either to the acid leaching 102 or to the acid purification 107. In the second reactor, which was operated at a temperature of about 930° C., acid was recovered through the condensation and absorption into two columns using mainly wash water from the acid leaching sector 102. Latent heat from this sector was recovered at the same time as large amounts of water, which limits net water input.

In the iron oxides productions and acid recovery 105 system, which comprises, aqueous solution from the crystallization 104 first undergoes a pre-concentration stage followed by processing in the hydrolyzer reactor. Here, hematite was produced during low temperature processing (about 165° C.). A recirculation loop was then taken from the hydrolyzer and is recirculated to the pre-concentrator, allowing the concentration of REE, Mg, K, and other elements. This recirculation loop, allows rare earth element chlorides and/or rare metal chlorides and various metal chlorides concentration to increase without having these products precipitating with hematite up to a certain extent.

Depending on acid balance in the plant, recovered acid is sent either directly to the 102 or 107 stage. Table 4 shows results obtained in stage 105.

TABLE 4 Hydrothermal acid recovery Flowrate from crystallization to 592 m³/h (design) HARP 600 m³/h (design) Operating hydrolyser 155-170° C. temperature Regenerated acid concentration 27.4% Regenerated acid flowrate 205.2 tph HCl Hematite total production rate 24 TPH (design) HCl recovery >99.8% Reflux (recirculation loop) rate in 56 tph between hydrolyzer and pre- concentrator Rare earth element chlorides ≈12.8 t/h and/or rare metal chlorides rate in recirculation loop Hematite quality obtained and/or projected Fe₂O₃ purity >99.5% Hydrolysable chlorides <0.2% Moisture Max 20% after filtration PSD 25-35 microns Density (bulk) 2-3 kg/l Typical chemical reaction in stage 105 2FeCl₃ + 3H₂O → Fe₂O₃ + 6HCl 155-170° C.

Table 5 shows results obtained in stage 106.

TABLE 5 Calcination Plant 106 Process characteristics: Two-stage circulating fluid bed (CFB) with pre-heating system Two-stage hydrochloric acid regeneration Production rate (practical) About 66 tph CFB feed rate 371 tph Typical chemical reaction occurring 2(AlCl₃•6H₂O) + Energy → Al₂O₃ + 6HCl + 9H₂O Typical alumina chemical composition obtained from aluminum chloride hexahydrate crystals being fed to calcination Component Weight distribution (%) Al₂O₃ 99.938 Fe₂O₃ 0.0033 SiO₂ 0.0032 Cr₂O₃ 0.0063 V₂O₅ 0.0077 Na 0.0190 MgO 0.0090 P₂O₅ 0.0039 K 0.0053 Ca 0.0020 MnO 0.0002 Free Cl⁻ Undetectable Rare Earth Elements and Rare Metals Extractions

The stream that was taken out of 105 recirculation then was treated for rare earth elements and are metals extraction 108, in which the reduction of the remaining iron back to iron 2 (Fe²⁺), followed by a series of solvent extraction stages, was performed. The reactants were oxalic acid, NaOH, DEHPA (Di-(2-ethylhexyl)phosphoric acid) and TBP (tri-n-butyl phosphate) organic solution, kerosene, and HCl were used to convert rare earth element chlorides and rare metals chlorides to hydroxides. Countercurrent organic solvent with stripping of solution using HCl before proceeding to specific calcination from the rare earth elements and rare metals in form of hydroxide and conversion to high purity individual oxides. An ion exchange technique is also capable of achieving same results as polytrimethylen terephtalate (PET) membrane.

Iron powder from 105, or scrap metal as FeO, can be used at a rate dependent on Fe³⁺ concentration in the mother liquor. HCl (100% wt) at the rate of 1 tph can be required as the stripped solution in REE Solvent Extraction (SX) separation and re-leaching of rare earth elements and/or rare metals oxalates.

Water of very high quality, demineralized or nano, at the rate of 100 tph was added to the strip solution and washing of precipitates.

Oxalic acid as di-hydrate at a rate of 0.2 tph was added and contributes to the rare earth elements and rare metals oxalates precipitation. NaOH or MgOH at a rate of 0.5 tph can be used as a neutralization agent.

DEHPA SX organic solution at the rate of 500 g/h was used as active reagent in rare earth elements separation while TBP SX organic solution at the rate of 5 kg/h is used as the active reagent for gallium recovery and yttrium separation. Finally, a kerosene diluent was used at the rate of approximately 2 kg/h in all SX section. Calcination occurs in an electric rotary furnace via indirect heating to convert contents to REE₂O₃ (oxides form) and maintain product purity.

Results of various tests made regarding stage 108 are shown in Table 6.

One line divided in subsections (5) to isolate the following elements using solvent extraction:

-   -   Ga₂O₃     -   Y₂O₃     -   Sc₂O₃     -   Eu₂O₃+Er₂O₃+Dy₂O₃     -   Ce₂O₃+Nd₂O₃+Pr₂O₃

Equivalent output earths oxides 166.14 kg/h Projected production as per pilot testing results Incoming Final extraction Feed (kg/h) individual (kg/h) Ga₂O₃ 15.66 11.98 Sc₂O₃ 9.06 8.11 Y₂O₃ 22.56 20.22 La₂O₃ 32.24 25.67 Ce₂O₃ 61.37 51.82 Pr₂O₃ 8.08 6.18 Nd₂O₃ 30.3 27.24 Sm₂O₃ 5.7 4.51 Eu₂O₃ 1.06 0.95 Gd₂O₃ 4.5 4.06 Dy₂O₃ 3.9 3.55 Er₂O₃ 2.1 1.86 Total 196.55 166.14 Global yield: 84.53%

Alternatively, stage 108 can be carried out as described in PCT/CA2012/000253 and/or PCT/CA2012000419.

The solution after stages 108 and 109 contained mainly MgCl₂, NaCl, KCl, CaCl₂, FeCl₂/FeCl₃, and AlCl₃ (traces), and then follows stage 111 Na, K, Ca that follows the MgO can be extracted in stage 110 by crystallization in a specific order; Na first, followed by K, and then Ca. This technique can be employed for example in the Israeli Dead Sea salt processing plant to produce MgO and remove alkali from the raw material.

HCl Regeneration

Alkali (Na, K), once crystallized, was sent and processed in the alkali hydrochloric acid regeneration plant 110 for recovering highly concentrated hydrochloric acid (HCl). The process chosen for the conversion can generate value-added products

Various options are available to convert NaCl and KCl with intent of recovering HCl. One example can be to contact them with highly concentrated sulfuric acid (H₂SO₄), which generates sodium sulphate (Na₂SO₄) and potassium sulfate (K₂SO₄), respectively, and regenerates HCl at a concentration above 90% wt. Another example, is the use of a sodium and potassium chloride brine solution as the feed material to adapted small chlor-alkali electrolysis cells. In this latter case, common bases (NaOH and KOH) and bleach (NaOCl and KOCl) are produced. The electrolysis of both NaCl and KCl brine is done in different cells where the current is adjusted to meet the required chemical reaction. In both cases, it is a two-step process in which the brine is submitted to high current and base (NaOH or KOH) is produced with chlorine (Cl₂) and hydrogen (H₂). H₂ and Cl₂ are then submitted to a common flame where highly concentrated acid in gas (100% wt.) phase is produced and can be used directly in the crystallization stage 104, or to crystallization stages requiring dry highly concentrated acid.

Magnesium Oxide

The reduced flow, which was substantially free of most elements (for example AlCl₃, FeCl₃, REE-Cl, NaCl, KCl) and rich in MgCl₂, was then submitted to the magnesium oxides plant 111. In the MgO, pyrohydrolysis of MgCl₂ and any other leftover impurities were converted into oxide while regenerating acid. The first step was a pre-evaporator/crystallizer stage in which calcium is removed and converted into gypsum (CaSO₄.2H₂O) by a simple chemical reaction with sulfuric acid, for which separation of MgO is required. This increases the capacity of MgO roasting and also energy consumption slightly, while substantially recovering HCl. The next step was the specific pyrohydrolysis of MgO concentrated solution by spray roasting. Two (2) main products were generated; MgO that was further treated and HCl (about 18% wt.), which was either recycled back to the upstream leaching stage 102 or to the hydrochloric acid purification plant (107 The MgO-product derived from the spray roaster can require further washing, purification, and finally calcining depending on the quality targeted. The purification and calcining can comprise a washing-hydration step and standard calcining step.

The MgO from the spray roaster is highly chemically active and was directly charged into a water tank where it reacts with water to form magnesium hydroxide, which has poor solubility in water. The remaining traces of chlorides, like MgCl₂, NaCl, dissolved in water. The Mg(OH)₂ suspension, after settling in a thickener, was forwarded to vacuum drum filters, which remove the remaining water. The cleaned Mg(OH)₂ is then forwarded into a calcination reactor where it is exposed to high temperatures in a vertical multi-stage furnace. Water from hydration is released and allows the transformation of the Mg(OH)₂ to MgO and water. At this point, the magnesium oxide was of high purity (>99%).

HCl Purification

The hydrochloric acid purification stage 107 is effective for purifying HCl regenerated from different sectors (for example 105, 106, 111) and to increase its purity for crystallization, whereas dry highly concentrated acid (>90% wt.) can be used as the sparging agent. Stage 107 also allowed for controlling the concentration of the acid going back to stage 102 (about 22 to about 32% wt.) and allows total acid and water balance. Total plant water balance is performed mainly by reusing wash water as absorption medium, as quench agent or as dissolution medium at the crystallization stages

For example, purification can be carried out by means of a membrane distillation process. The membrane distillation process applied here occurs when two aqueous liquids with different temperatures are separated through a hydrophobic membrane. The driving force of the process was supplied by the partial pressure vapour difference caused by the temperature gradient between these solutions. Vapour travels from the warm to the cold side. Without wishing to be bound to such a theory, the separation mechanism was based on the vapour/liquid equilibrium of the HCl/water liquid mixture. Practical application of such a technology has been applied to HCl/water, H₂SO₄/water systems and also on large commercial scales on aqueous solution of sodium chloride with the purpose of obtaining potable water from seawater and nano water production. Therefore membrane distillation was a separation process based on evaporation through a porous hydrophobic membrane. The process was performed at about 60° C. and was effective to recover heat from the 104 and 102 stage with an internal water circulation loop, in order to maintain a constant incoming temperature to the membranes. For example, eight membranes of 300,000 m² equivalent surface area can be used per membrane to obtain a concentration of HCl well above the azeotropic point (i.e. >36%) of the ≈750 m³/h and final 90% concentration is then obtained through pressure distillation (rectification column).

Purification of HCl by processing thus regenerated acid through hydrophobic membrane and separating water from HCl; therefore increasing HCl concentration up to about 36% (above azeotropic point) and therefore allowing with a single stage of rectification through a pressure stripping column to obtain >90% in gaseous phase, for crystallization stage (sparging); and therefore controlling acid concentration into crystallization stages up to 30-35%_((aq)).

As indicated stage 107 was operated at about 60° C. and heat input provided by heat recovery from stages 102 to 110. Rectification column was operated at about 140° C. in the reboiler part. Net energy requirement was neutral (negative in fact at −3.5 Gj/t Al₂O₃) since both systems were in equilibrium and in balance.

For example, the acid purification can be carried out by using adsorption technology over an activated alumina bed. In continuous mode, at least two adsorption columns are required to achieve either adsorption in one of them and regeneration in the other one. Regeneration can be performed by feeding in counter-current a hot or depressurized gas. This technology will result in a purified gas at 100% wt.

For example, the acid purification can be made by using calcium chloride as entrainer of water. A lean hydrochloric acid solution is contacted with a strong calcium chloride solution through a column. The water is then removed from the hydrochloric acid solution and 99.9% gaseous HCl comes out of the process. Cooling water and cryogenic coolant is used to condense water traces in the HCl. The weak CaCl₂ solution is concentrated by an evaporator that ensures the recuperation of calcium chloride. Depending on the impurities in the incoming HCl solution feed to the column, some metals can contaminate the calcium chloride concentrated solution. A precipitation with Ca(OH)₂ and a filtration allows the removal of those impurities. The column can operate for example at 0.5 barg. This technology can allow for the recuperation of 98% of the HCl.

Table 7 shows the results obtained concerning the process shown in FIG. 6.

Composition Stage 101 Stage 102 Stage 106 Stage 105 MgO Stage 107 Stage 108 TOTAL PRODUCED (% wt) Yield (%) Yield (%) Yield (%) Yield (%) tpy Yield (%) Yield (%) Yield (%) Yield (%) Main constituents SiO₂ — 99.997% — — — — — — 99.997%  Al —  98.02% 95.03% — — — — — 95.03% Fe — 100.00% — 92.65% — — — — 92.65% Mg — 99.998% — — 29,756 92.64% — — 92.64% Ca — 99.998% — — — — — — 98.28% Na — 99.998% — — — — — — 92.76% K — 100.00% — — — — — — 93.97% Others incl. H₂O — — — — — — — — RE/RM —  99.80% — 92.32% — — — 84.67% 84.67% By-Products NaOH — — — — 68,556 — — — — NaOCl — — — — 9,269 — — — — KOH — — — — 73,211 — — — — KOCl — — — — 9,586 — — — — CaSO₄ — — — — 46,837 — — — — Reactants H₂SO₄(*) — — — — 19,204 — — — — Fresh HCl M-UP — — — — — — 99.75% — 99.75% Total —  98.55% 95.03% 256,419 92.64% 99.75% 84.67%

Tables 8 to 26 show results obtained concerning the products made in accordance with the process shown in FIG. 6 in comparison with standard of the industry.

TABLE 8 Chemical composition of obtained alumina Element % Weight Standard used in industry Al₂O₃ 99.938 98.35 min Fe₂O₃ 0.0033 0.0100 SiO₂ 0.0032 0.0150 TiO₂ 0.0003 0.0030 V₂O₅ 0.0008 0.0020 ZnO 0.0005 0.0030 Cr₂O₃ 0.0003 N/A MgO 0.0090 N/A MnO 0.0002 N/A P₂O₅ 0.0039 0.0010 Cu 0.0030 N/A Ca 0.0020 0.0030 Na 0.0190 0.4000 K 0.0053 0.0150 Li 0.0009 N/A Ba <0.00001 0.0000 Th <0.000001 0.0000 U <0.000001 0.0000 Free Cl⁻ Not detectable 0.0000 LOI <1.0000 <1.0000 

TABLE 9 Physical properties of obtained alumina Property Orbite Alumina Standard used in industry PSD < 20 μm  5-10% N/A PSD < 45 μm 10-12% <10% PSD > 75 μm 50-60% N/A SSA (m²/g) 60-85  60-80 Att. Index 10-12% <10% α Al₂O₃ 2-5%  <7-9%

TABLE 10 Chemical composition of obtained hematite Element % Weight Fe₂O₃ >99.5% Hydrolysable elements <0.2%

TABLE 11 Physical properties of obtained hematite* Property Orbite hematite PSD_(mean) 25-35 μm Density (bulk) 2000-3000 kg/m³ Humidity after filtration <10% *Material can be produced as brickets

TABLE 12 Chemical composition of obtained silica Element % Weight SiO₂ >99.7 Al₂O₃ <0.25% MgO ≈0.1% Fe₂O₃ ≈0.1% CaO ≈0.01% Na₂O <0.1% K₂O <0.1% Note: Product may have unbleached cellulose fiber filter aid. Cellulose wood flour.

TABLE 13 Physical properties of obtained silica Property Orbite silica PSD_(mean) 10-20 μm Specific surface area 34 m²/g Density (bulk) 2000-2500 kg/m³ Humidity after filtration <40%

TABLE 14 Purity of obtained rare earth element oxides Element Purity (%) Ga₂O₃ >99% Sc₂O₃ Y₂O₃ La₂O₃ Ce₂O₃ Pr₂O₃ Nd₂O₃ Sm₂O₃ Eu₂O₃ Gd₂O₃ Dy₂O₃ Er₂O₃ Physical properties of obtained REE-O/RM-O Property Orbite REE-O/RM-O PSD_(mean) 2-30 μm Density 5500-13000 kg/m³ LOI <1%

TABLE 15 Chemical composition of obtained MgO Element Typical Specification MgO 99.0⁺ 98.35 min CaO 0.0020 0.83 SiO₂ 0.0000 0.20 max B₂O₃ 0.0000 0.02 max Al₂O₃ 0.0300 0.12 max Fe₂O₃ 0.0160 0.57 max MnO₂ <0.14 0.14 max LOI 0.7% <1% 

TABLE 16 Physical properties of obtained MgO Property Orbite MgO PSD_(mean) 10 μm Density N/A LOI 650 kg/m³

TABLE 17 Chemical composition of obtained NaOH Element % Weight Sodium hydroxide 32% Water 68%

TABLE 18 Physical properties of obtained NaOH Property Sodium hydroxide (NaOH) Physical state Liquid Vapour pressure 14 mmHg Viscosity >1   Boiling point 100° C. Melting point 0° C. Specific gravity 1.0

TABLE 19 Chemical composition of obtained sodium hypochlorite (bleach) Element % Weight Sodium hypochlorite 12% Sodium hydroxide <1% Water >80% 

TABLE 20 Physical properties of obtained NaOCl Property Sodium hypochlorite (NaOCl) Physical state Liquid Vapour pressure 1.6 kPa Viscosity N/A Boiling point 100° C. Melting point −3° C. Specific gravity 1.2

TABLE 21 Chemical composition of obtained potassium hydroxide Element % Weight Potassium hydroxide 32% Water 68%

TABLE 22 Physical properties of obtained potassium hydroxide Property KOH Physical state Liquid Vapour pressure 17.5 mmHg Viscosity N/A Boiling point 100° C. Melting point N/A Specific gravity 1.18

TABLE 23 Chemical composition of obtained potassium hypochlorite (KOCl) Element % Weight Potassium hypochlorite 12% Potassium hydroxide <1% Water >80% 

TABLE 24 Physical properties of obtained potassium hypochlorite Property KOCl Physical state Liquid Vapour pressure N/A Viscosity N/A Boiling point 103° C. Melting point N/A Specific gravity >1.0

TABLE 25 Chemical composition of obtained calcium sulphate dihydrate Element % Weight Calcium sulphate dihydrate 100%

TABLE 26 Physical properties of obtained calcium sulphate dihydrate Property Orbite CaSO₄•2H₂O Physical state Solid Specific gravity 2.32

In order to demonstrate the versatility of the processes of the present disclosure, several other tests have been made so as to shown that these processes can be applied to various sources of starting material.

EXAMPLE 6

Another starting material has been used for preparing acidic compositions comprising various components. In fact, a material that is a concentrate of rare earth elements and rare metals (particularly rich in zirconium) has been tested. Table 27 shows the results of the leaching carried out on such a starting material using a similar process as shown in FIGS. 1, 3, 6 and 7 and as detailed in Examples 1, 2 and 5. It can thus be inferred from the results shown in Table 27 that the various components present in the leaching (various metals such as aluminum, iron, magnesium as well as rare earth elements and rare metals) can be extracted from the obtained leaching composition and that they can eventually be isolated by the processes of the present disclosure such as, for example, those presented in Examples 1, 2 and 5.

EXAMPLE 7

Other tests have been made in a similar manner as described in Example 6. In the present example, carbonatite has been used as a starting material. (see Table 28 below).

TABLE 27 Tests made on a zirconium rich material. Composition Average measure and/ measured Extraction O All Raw or evaluated for testing rate measured Orbite process material (% wt.) (% wt .) (ALP) (%) recovery (%) Al₂O₃ 6.12 6.12 89.65 86.97 Fe₂O₃ 15.80 15.80 99.50 97.51 SiO₂ 36.00 36.00 0.000 99.997 MgO 3.08 3.08 99.75 92.66 Na₂O 1.13 1.13 99.50 99.50 K₂O 2.12 2.12 99.50 99.50 CaO 6.10 6.10 99.50 99.00 S total 0.22 0.22 100.00 F 1.98 1.98 99.50 99.00 TiO₂ 0.13 0.13 0.000 99.03 V₂O₅ 0.00 0.00 98.00 96.04 P₂O₅ 1.10 1.10 98.00 96.04 MnO 0.43 0.43 98.00 96.04 ZrO₂ 12.43 12.43 22.70 20.43 Cr₂O₃ 0.00 0.00 0.00 0.00 Ce₂O₃ 3.05 3.045 97.31 92.98 La₂O₃ 1.34 1.337 99.55 92.68 Nd₂O₃ 1.55 1.551 98.40 94.79 Pr₂O₃ 0.37 0.375 99.75 97.52 Sm₂O₃ 0.15 0.151 88.75 84.80 Dy₂O₃ 0.09 0.089 80.35 76.77 Er₂O₃ 0.03 0.030 72.60 69.37 Eu₂O₃ 0.03 0.027 85.57 81.76 Gd₂O₃ 0.21 0.205 82.85 79.16 Ho₂O₃ 0.01 0.013 77.10 73.67 Lu₂O₃ 0.00 0.003 60.15 57.47 Tb₂O₃ 0.02 0.022 78.05 74.58 Th 0.02 0.022 88.10 84.18 Tm₂O₃ 0.00 0.004 66.85 63.88 U 0.01 0.014 81.90 78.26 Y₂O₃ 0.30 0.300 72.70 69.46 Yb₂O₃ 0.02 0.023 62.80 60.01 Ga₂O₃ 0.02 0.016 96.90 92.59 Sc₂O₃ 0.00 0.003 95.00 90.77 LOI (inc. 6.122023973 6.12 water)

TABLE 28 Tests made on carbonatite Composition Average measure and/ measured Extraction O All Raw or evaluated for testing rate measured Orbite process material (% wt.) (% wt.) (ALP) (%) recovery (%) Al₂O₃ 0.70 0.70 84.31 81.61 Fe₂O₃ 11.22 11.22 94.14 92.15 SiO₂ 2.11 2.11 0.00003 99.997 MgO 6.50 6.500 100 96.25 Na₂O 0.07 0.07 92.54 90.55 K₂O 0.18 0.181 37.33 37.33 CaO 16.51 16.51 100 98.00 TiO₂ 0.00 0.000 0.00000 100.000 V₂O₅ 0.00 0.000 0 100.000 P₂O₅ 0.00 0.000 0 100.000 MnO 0.00 0.000 0 100.000 ZrO₂ 0.00 0.000 0 100.000 Cr₂O₃ 0.00 0.000 0 100.000 Ce₂O₃ 1.19 1.195 64.04 61.190 La₂O₃ 0.46 0.463 63.86 61.018 Nd₂O₃ 0.45 0.448 81.46 77.835 Pr₂O₃ 0.14 0.142 67.59 64.582 Sm₂O₃ 0.03 0.033 65.32 62.413 Dy₂O₃ 0.00 0.000 78.12 74.644 Er₂O₃ 0.00 0.000 86.15 82.316 Eu₂O₃ 0.01 0.007 66.45 63.493 Gd₂O₃ 0.01 0.013 54.46 52.037 Ho₂O₃ 0.00 0.000 83.12 79.421 Lu₂O₃ 0.00 0.000 88.86 84.906 Tb₂O₃ 0.00 0.001 41.42 39.577 Th 0.06 0.065 Tm₂O₃ 0.00 0.000 90.70 86.664 U 0.01 0.007 Y₂O₃ 0.00 0.000 84.68 80.912 Yb₂O₃ 0.00 0.000 85.11 81.323 Ga₂O₃ 0.00 0.000 0 0.000 Sc₂O₃ 0.00 0.000 0 0.000 LOI (inc. 60.33 water)

It can thus be inferred from the results shown in Table 28 that the various metals, rare earth elements and rare metals extracted present in the obtained leaching composition can eventually be isolated by the processes of the present disclosure such as, for example, those presented in Examples 1, 2 and 5.

EXAMPLE 8

Test have been made for using fly ash as starting material. The results are shown below in Tables 29, 30 and 31.

TABLE 29 Leaching conditions for fly ash Leaching Operating Conditions Processing Reactor Pressure Temperature Time Acid Ratio Volume 75-80 psi 150-165° C. 420 Stoichiom- 16 gallons minutes etry + 30%

TABLE 30 Fly ash used Fly Ash Masse In 2600 Masse Out  302 % H2O  30%

TABLE 31 Results - leaching of fly ash Recovery Yield % Al K Na Fe Ca Si Initial % 8.02 1.21 0.42 8.27 1.65 13.9 compound kg 208.52 31.45 10.92 215.02 42.9 361.4 Cake % 9.15 1.15 0.26 1.75 0.3 36.9 kg 19.3431 2.4311 0.54964 3.6995 0.6342 78.0066 % recovery 90.72% 92.27% 94.97% 98.28% 98.52% 78.42% * 0% MgO initially

It can thus be seen that fly ash has been successfully leached with HCl, thereby allowing for good yields with respect to the recovery of the various components present in Fly ash. These various products or components present in the obtained leachate can thus be all isolated and eventually transformed as previously indicated in the processes of the present disclosure. The obtained leachate can then be treated as described in the processes of the present disclosure. The leaching of example 8 can be considered, for example, as the leaching 2 of FIG. 1 or FIG. 3; the leaching 102 of FIG. 6 or FIG. 7, etc. For example, the leachate obtained in Example 8 can then be treated as shown in FIGS. 1, 3, 6 and 7.

EXAMPLE 9

Other tests have been made for using another alternative source of fly ash. A similar process was used. The initial measured conditions were:

TABLE 32 Fly Ash initial composition Element Composition measured (% wt) SiO₂ 29.73 Al₂O₃ 15.15 Fe₂O₃ 11.82 CaO 2.31 Na₂O 0.57 K₂O 1.46

The samples were leached in batch mode at 75 psig (150° C.) for a 6 hours duration at stoechiometry +5% excess Hcl (20% wt).

The following extraction yields were measured at the leaching stage:

TABLE 33 Leaching extraction yield measured Raw element Extraction measured (% wt) Al₂O₃ 96.1 Fe₂O₃ 98.5 N 95.7 Na₂O K₂O 93.4 CaO 98.7

After processing through main steps of process (see for example FIG. 6), the following yields were measured.

TABLE 34 Global recovery yield Element Global recovery (% wt) Al₂O₃ 93.4 Fe₂O₃ 96.5 SiO₂ 99.99 No2₂O 93.7 K₂O 93.4 CaO 96.8 Main characteristics of produced alumina were:

-   -   Chemical composition: 99.4%;     -   PSD dp₅₀: 63 um;     -   α Al₂O₃: 2%; and     -   Bulk density: 0.63.

EXAMPLE 10

Other tests was performed on another alternative source of material always using the same process as per previous examples. The initial composition measured was:

TABLE 35 Fly Ash initial composition Element Composition measured (% t wt) SiO₂ 44.9 Al₂O₃ 22.1 Fe₂O₃ 21.0 CaO 4.1 Na₂O 0.7 K₂O 2.4

The samples were leached in hatch mode at 160° C. (80 psig) for a 6 hours duration at stoichiometry +10% Hcl excess (20% wt).

The following extraction yields were measured at the leaching stage.

TABLE 36 Leaching extraction yield measured Raw element Extraction measured (% wt) Al₂O₃ 97.6 Fe₂O₃ 99.5 Na₂O 91.1 K₂O 93.3 CaO 94.9

After processing through main steps of continuous process (see FIG. 6) the following yield were measured:

TABLE 37 Global recovery yield Element Global recovery (% wt) Al₂O₃ 94.9 Fe₂O₃ 97.5 SiO₂ 99.99 Na2O 89.1 K₂O 93.3 CaO 93.0

The applicants have now discovered fully integrated and continuous processes with substantially total hydrochloric acid recovery for the extraction of alumina and other value added products from various materials that contain aluminum (clay, bauxite, aluminosilicate materials, slag, red mud, fly ash etc.) containing aluminum. In fact, the processes allows for the production of substantially pure alumina and other value added products purified such as purified silica, pure hematite, pure other minerals (ex: magnesium oxide) and rare earth elements products. In addition, the processes do not require thermal pre-treatment before the acid leach operation. Acid leach can be carried out using semi-continuous techniques with high pressure and temperature conditions and very high regenerated hydrochloric acid concentration. The processes can also be carried out at atmospheric pressure. In addition, the processes do not substantially generate any residues not sellable, thus eliminating harmful residues to environment like in the case of alkaline processes.

The advantage of the high temperature calcination stage, in addition for allowing to control the α-form of alumina required, can be effective for providing a concentration of hydrochloric acid in the aqueous form (>38%) that is higher than the concentration of HCl at the azeotropic point and thus providing a higher incoming HCl concentration to the leaching stage. The calcination stage hydrochloric acid network can be interconnected to two (2) crystallization systems and by pressure regulation excess HCl can be being absorbed at the highest possible aqueous concentration. The advantage of having a hexahydrate chloride with low moisture content (<2%) incoming feed allows for a continuous basis to recover acid at a concentration that is higher than the azeotropic concentration. This HCl balance and double usage into three (3) common parts of the processes and above azeotropic point is a substantial advance in the art.

Another advantage is when the use is made of the incoming chemistry (ferric chloride) to the iron oxide and hydrochloric acid recovery unit where all excess heat load from any calcination part, pyrohydrolysis and leaching part is being recovered to preconcentrate the mother liquor in metal chloride, thus allowing, at very low temperature, the hydrolysis of the ferric chloride in the form of very pure hematite and the acid regeneration at the same concentration than at its azeotropic point.

A further major advantage of the processes of the present disclosure at the ferric chloride hydrolysis step can be the possibility to concentrate rare earth elements in form of chlorides at very high concentration within the hydrolyser reactor through an internal loop between hydrolyzer and crystallization. The advantage is that the processes of the present disclosure benefit from the various steps where gradual concentration ratios are applied. Thus, at this stage, in addition to an internal concentration loop, having the silica, the aluminum, the iron and having in equilibrium a solution close to saturation (large amount of water evaporated, no presence of free hydrochloric acid) allows for taking rare earth elements and non-hydrolysable elements in parts per million into the incoming feed and to concentrate them in high percentage directly at the hydrolyser after ferric chloride removal Purification of the specific oxides (RE-O) can then be performed using various techniques when in percentage levels. The advantage can be doubled here: concentration at very high level of rare earth elements using integrated process stages and most importantly the approach prevents from having the main stream (very diluted) of spent acid after the leaching step with the risk of contaminating the main aluminum chloride stream and thus affecting yields in Al₂O₃. Another important improvement of the art can be that on top of being fully integrated, selective removal of components allows for the concentration of rare earth elements to relatively high concentration (percentages).

Another advantage of the processes can be again a selective crystallization of MgCl₂ through the sparging of HCl from either the alumina calcination step or the magnesium oxide direct calcination where in both cases highly concentrated acid both in gaseous phase or in aqueous form are being generated. As per aluminum chloride specific crystallization, the direct interconnection with the calcination reactor, the HCl gas very high concentration (about 85 to about 95%, about 90 to 95% or about 90% by weight) allows for exact adjustment in continuous of the crystallizer based on quality of magnesium oxide targeted. Should this process step (MgO production or other value added metal oxide) be required based on incoming process feed chemistry, the rare earth elements extraction point then be done after this additional step; the advantage being the extra concentration effect applied.

The pyrohydrolysis can allow for the final conversion of any remaining chloride and the production of refined oxides that can be used (in case of clay as starting material) as a fertilizer and allowing the processing of large amount of wash water from the processes with the recovery of hydrochloric acid in close loop at the azeotropic point for the leaching step. The advantage of this last step can be related to the fact that it does totally close the process loop in terms of acid recovery and the insurance that no residues harmful to the environment are being generated while processing any type of raw material, as previously described.

A major contribution to the art can be that the proposed fully integrated processes of the present disclosure are allowing, among others, the processing of bauxite in an economic way while generating no red mud or harmful residues. In addition to the fact of being applicable to other natural of raw materials (any suitable aluminum-containing material or aluminous ores), the fact of using hydrochloric acid total recovery and a global concentration that can be higher than the concentration at the azeotropic point (for example about 21% to about 38%), the selective extraction of value added secondary products and compliance (while remaining highly competitive on transformation cost) with environmental requirements, represent major advantages in the art.

The processes of the present disclosure can provide fully continuous and economical solutions that can successfully extract alumina from various type of materials while providing ultra pure secondary products of high added value including highly concentrated rare earth elements and rare metals. The technology described in the present disclosure can allow for an innovative amount of total acid recovery and also for a ultra high concentration of recovered acid. When combing it to the fact that combined with a semi-continuous leaching approach that favors very high extraction yields and allows a specific method of crystallization of the aluminum chloride and concentration of other value added elements. These processes can also allow for preparing aluminum with such a produced alumina.

For example, through the type of equipment that can be used (for example vertical roller mill) and its specific operation, raw material grinding, drying and classifying can be applicable to various kinds of material hardness (furnace slag for example), various types of humidity (up to 30%) and incoming particle sizes. The particle size established can provide the advantage, at the leaching stage, of allowing efficient contact between the minerals and the acid and then allowing faster kinetics of reaction. Particles size employed can be effective to reduce drastically the abrasion issue and allows for the use of a simplified metallurgy/lining when in contact with hydrochloric acid.

A further advantage of the processes of the present disclosure can be the combined high temperature and high incoming hydrochloric acid concentration. Combined with a semi continuous operation where the free HCl driving force can be used systematically, iron and aluminum extraction yields do respectively reach 100% and 98% in less than about 40% of the reference time of a basic batch process. Another advantage of higher HCl concentration than the concentration at azeotropic point can be the potential of capacity increase. Again a higher HCl concentration than the concentration of HCl at the azeotropic point and the semi-continuous approach can represent a substantial advance in the art.

Another advantage in that technique used for the mother liquor separation from the silica after the leaching stage countercurrent wash, can be that band filters provide ultra pure silica with expected purity exceeding 96%.

The crystallization of AlCl₃ into AlCl₃.6H₂O using dried, cleaned and highly concentrated gaseous HCl as the sparging agent can allow for a pure aluminum chloride hexahydrate with only few parts per million of iron and other impurities. A minimal number of stages can the be required to allow proper crystal growth.

The direct interconnection with the calcination of AlCl₃.6H₂O into Al₂O₃ which can produce very high concentration of gas allows the exact adjustment in continuous of the HCl concentration within the crystallizer and thus proper control of the crystal growth and crystallization process.

It was thus demonstrated that the present disclosure provides fully integrated processes for the preparation of pure aluminum oxide using a hydrochloric acid treatment while producing high purity and high quality products (minerals) and extracting rare earth elements and rare metals.

While a description was made with particular reference to the specific embodiments, it will be understood that numerous modifications thereto will appear to those skilled in the art. Accordingly, the above description and accompanying drawings should be taken as specific examples and not in a limiting sense. 

What is claimed is:
 1. A process for treating raw fly ash, said process comprising: optionally a pre-leaching treatment that consists of reducing the particle size of said raw fly ash; leaching said raw fly ash with HCl so as to obtain a leachate comprising aluminum ions and iron ions and a solid, and separating said solid from said leachate; reacting said leachate with HCl so as to obtain a liquid comprising iron ions and a precipitate comprising said aluminum ions in the form of AlCl₃, and separating said precipitate from said liquid; and heating said precipitate under conditions effective for converting AlCl₃ into Al₂O₃ and optionally recovering gaseous HCl so-produced.
 2. The process of claim 1, wherein said fly ash is leached with HCl having a concentration of about 25 to about 45 weight %.
 3. The process of claim 2, wherein said process further comprises recycling said gaseous HCl so-produced by contacting it with water so as to obtain a composition having a concentration of about 25 to about 45 weight % and using said composition for leaching said fly ash.
 4. The process of claim 1, wherein said fly ash is leached with HCl having a concentration of about 25 to about 45 weight % at a temperature of about 125 to about 225° C.
 5. The process of claim 4, wherein said fly ash is leached at a pressure of about 4 to about 10 barg (about 400 KPag to about 1000 KPag).
 6. The process of claim 5, wherein said process is effective for avoiding producing red mud.
 7. The process of claim 1, wherein said fly ash is leached with HCl having a concentration of about 25 to about 45 weight % at a temperature of about 160 to about 190° C.
 8. The process of claim 1, wherein said fly ash is leached with HCl having a concentration of about 18 to about 45 weight %.
 9. The process of claim 1, wherein said fly ash is leached with HCl having a concentration of about 18 to about 45 weight % at a temperature of about 125 to about 225° C.
 10. The process of claim 1, wherein said recycled gaseous HCl so-produced is contacted with water so as to obtain said composition having a concentration between 18 and 36 weight %.
 11. The process of claim 1, wherein said process comprises reacting said leachate with gaseous HCl so as to obtain said liquid and said precipitate comprising said aluminum ions, said precipitate being formed by crystallization of AlCl₃·6H₂O.
 12. The process of claim 11, wherein during said crystallization of AlCl₃·6H₂O, said liquid is maintained at a concentration of HCl of about 25 to about 35% by weight.
 13. The process of claim 12, wherein said crystallization is carried out at a temperature of about 45 to about 65° C.
 14. The process of claim 11, wherein said process comprises heating said precipitate at a temperature of about 350° C. to about 500° C. for converting AlCl₃·6H₂O into Al₂O₃.
 15. The process of claim 1, wherein said process comprises reacting said leachate with HCl recovered during said processs and having a concentration of at least 30% by weight as to obtain said liquid and said precipitate comprising said aluminum ions, said precipitate being formed by crystallization of AlCl₃.6H₂O.
 16. The process of claim 15, wherein said crystallization is carried out at a temperature of about 45 to about 65° C.
 17. The process of process of claim 1, wherein said process comprises converting AlCl₃·6H₂O into Al₂O₃ by carrying out a calcination of AlCl₃.6H₂O, said calcination comprising steam injection.
 18. The process of process of claim 17, wherein said steam is overheated.
 19. The process of claim 1, wherein said fly ash is leached at a pressure of about 4 to about 10 barg (about 400 KPag to about 1000 KPag).
 20. A process for preparing aluminum, said process comprising : optionally a pre-leaching treatment that consists of reducing the particle size of raw fly ash; leaching said raw fly ash with HCl so as to obtain a leachate comprising aluminum ions and iron ions and a solid, and separating said solid from said leachate; reacting said leachate with HCl so as to obtain a liquid comprising iron ions and a precipitate comprising said aluminum ions in the form of AlCl₃, and separating said precipitate from said liquid; heating said precipitate under conditions effective for converting AlCl₃ into Al₂O₃ and optionally recovering gaseous HCl so-produced; and converting said Al₂O₃ into aluminum. 